Distribution Category - UNT Digital Library/67531/metadc...NUCLEAR PHYSICS RESEARCH Introduction 1 1. MEDIUM-ENERGY PHYSICS RESEARCH 3 A. STUDY OF PION REACTION MECHANISMS 5 ... g

Distribution Category:Physics -General

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ANL-83-25

AN--83-25

DES3 014014

ARGONNE NATIONAL LABORATORY9700 South Cass Avenue

Argonne, Illinois 60439

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PHYSICS DIVISION ANNUAL REVIEW

1 APRIL 1982--31 MARCH 1983

Donald S. Gemmell

Division Director

June 1983

1id . . ph

Preceding Annual Reviews

ANL-80 -94ANL-81-79ANL-82-74

1979-19801980-19811981-1982

FOREWORD

The Physics Division Annual Review presents a

broad but necessarily incomplete view of the research

activities within the Division for the year ending in

March 1983.

At the back of this report a complete list of

publications along with the Division roster can be

found.

TABLE OF CONTENTS

NUCLEAR PHYSICS RESEARCH

Introduction 1

1. MEDIUM-ENERGY PHYSICS RESEARCH 3

A. STUDY OF PION REACTION MECHANISMS 5

a. Study of the Pion Absorption Mechanism in 3 He 5through the (Tr+,2p) and (1~, pn) Reactions

b. Study of mow-Energy Pion Absorption in 3He 6

c. Study of Pion Absorption Through the A(Tr,p)X 8Reaction at T, = 500 MeV

d. Survey of Inclusive Pion Scattering Near the A339Resonance

e. Inclusive Pion Charge-Exchange Reactions 11

f. Isospin Dependence of the 18,160(7 , wo) Reactions 13

g. Study of the (Tr,Irp) Reaction and Quasifree 15Scattering in 4 He

h. Measurement Near Threshold of 9Be(3He,IT) to the 15A = 12 Isobaric Triplet by Recoil Detection

i. The A Dependence of the (e,e'p) Reaction in the 16Quasifree Region

B. NUCLEAR STRUCTURE STUDIES 17

a. Inelastic Scattering of Pions by 10B and 1B 17

b. Inelastic Pion Scattering from 14 N 19

c. Excitation of 8-, Particle-Hole States in 54Fe 20

d. Iso alar Quenching in the Excitation of 8 States 22in Cr

e. Excitation of 8 States in 52Cr 22

f. Polarized Proton Scattering from 26Mg 23

V

Transverse Electron Scattering by 2 6Mg

Inelastic Scattering of p + 48Ca at 160 MeV

Study of the 4He(1~, r+) Reaction at Small Angles

Discrete States from Pion Double-Charge-Exchange onHeavy Nuclei

C. TWO-NUCLEON PHYSICS WITH PIONS AND ELECTRONS

a. Energy and Angular Dependence of Tensor Polarizationin Pion-Deuteron Elastic Scattering

b. Tensor Polarization in Electron-Deuteron ElasticScattering

c. Feasibility Study of Electron Scattering Experimentswith a Tensor Polarized Deuterium Target in anElectron Storage Ring

d. Deuteron Tensor Polarimeter Development

e. Photoneutron Physics

D. WEAK

a.

b.

c.

d.

e.

f.

g.

h.

INTERACTIONS

Neutrino Oscillations at LAMPF

Beta Decay of Polarized Nuclei and the DecayAsymmetry of 8Li

A Test of V-A Positron Decay

The Beta Decay Rate of 1 6 N(J - 0', 120 keV); MesonExchange Currents and the Induced PseudoscalarCoupling Constant

0+ + 0- Beta Decay of 1 6 C Ground State

The B anching Ratio to the 160 Ground State forthe 19N Ground State

Neutron Beta Decay

Study of the 1 0 B(2-, 5.11 MeV) and lOB(2+, 5.16 MeV)Levels

vi

g."

h.

is

is

Page

25

25

27

27

29

29

30

32

33

33

35

35

36

39

39

40

44

45

47

E. PARTICLE SEARCHES

a. A Cryogenic Experiment for the Detection ofFractionally-Charged Particles

b. A Search for Super-Heavy Particles in Cosmic Rays

c. A Search for Axions from Nuclear Decays

F. MEASUREMENT OF THE ELECTRIC DIPOLE MOMENT OF THE NEUTRON

G. GeV ELECTRON MICROTRON

a. Workshop on High-Resolution a'd Large-AcceptanceSpectrometers

b. Microtron Development

II. RESEARCH AT THE TANDEM AND SUPERCONDUCTING LINAC ACCELERATOR

A. HIGH ANGULAR MOMENTUM STATES IN NUCLEI

a. Gamma Spectroscopy at Very High Spin in 147Gd

b. Shape Change in 153Dy

c. Lifetime Measurements in 154Dy

d. Shape Changes at High Spin in 155Er

e. Lif mc 5 easurements of Continuum Statesin ' Er

f.

g.

h.

i.

j.

Measurement of Feeding Times in 152Dy

Yrast Population Patterns in a Wide Range of Nuclei

The (nh11 /2)6 Spectrum in 152Yb

Spectroscopy of 100Cd

Prolate and Oblate Rotational Bands in 186Hg

vii

Page

49

49

50

51

53

55

58

58

59

61

61

63

64

65

66

67

67

68

69

69

Page

B. FUSION OF HEAVY IONS 73

u. Fusion of 6 4Ni + 112, 11 4 ,116,1 1 8 ,1 2 0 ,12 2 ,1 2 4 Sn 73

b. Fusion of 5 8Ni + 112,1 1 4,116, 1 1 8 ,12 0,12 2 ,12 4 Sn 75

c. Fission of 6 4Ni + 112,114,116,118,120,122,1245n 75

d. Delayed Alpha-Decay of Evaporation Residues Formed 77in Fusion Reactions

e. Atomic Charge States of Evaporation Residues 79

f. Prompt Compound-Nuclear K X-rays in Fusion Reactions 79Induced by a Heavy Projectile

g. Suppression of Neutron Emission in "Cold" Heavy-Ion 80Fusion

C. REACTION MECHANISMS AND DISTRIBUTION OF REACTION 83STRENGTHS

a. Reactions o Resolved States of Nonfusion Channels 83for 160 + 8Ca at Elab = 158.2 MeV

b. Inelastic Scattering tpd Sine-Nucleon Transfer 83Reactions Induced by 0 on Ca at Elab(1 0) =150 MeV

c. Measurement s of Evaporation Residues Produced 86in 160 + 2 Mg at 4 S Elab(160) S 9.5 MeV/A

d. Time-of-Flig~ Measurements of Evaporation Residues 88Produced in Si-Induced Reactions

e. Fusion Cross Section Measurements for 20Ne + 40Ca at 90

Elab(2 0Ne) - 150 and 220 MeV

f. Study of Direct Reactions in the System 37C1 + 20 8Pb 91at Elab = 250 MeV

g. Spectroscopic Studies of 23 4Th with the (180,160) 91Reaction

h. Large Neutro -Transfer Cross Sections Observed 94in SNi and 8Ti Induced reaction on 208Pb

i. Observation of Characteristic Gamma Rays from Quasi- 97Elgtic and Deep-Inelastic Fragments in the 5 8Ni+ Ni Reaction

Page

D. ACCELERATOR MASS SPECTROMETRY 99

a. Measurement of the Half-Life of 4 4 Ti via Accelerator 99Mass Spectrometry

b. Search for Doubly-Charged Negative Ions via 102

Accelerator Mass Spectrometry

c. Accelerator Mass Spectrometry of 4 1 Ca 103

d. Measurement of the Half-Life of 6 0 Fe Using the 107Tandem-Linac System as an Accelerator MassSpectrometer

E. SELECTED NUCLEAR SPECTROSCOPY AT THE TANDEM-LINAC 111

a. Laser Spectroscopy of Radioactive Atoms 111

b. Search for Transient Electric Field Gradient Acting 112on Fast-Moving Ions in Solids

c. The 7 Be(p,Y)8Be Reaction 112

d. Resonances in 7Be(a,Y) and 7Li(a,Y) 114

e. The 7Be Decay Branching Ratio 115

F. EQUIPMENT DEVELOPMENT AT THE TANDEM-LINAC FACILITY 11

a. Ray-Tracing Corrections for the Focal-Plane Counter 117at the Spectrograph

b. Test of the Large Focal-Plane Counter for the Linac 119Magnetic Spectrograph

c. A AE-E Detector for Fusion Measurements 119

d. Modifications to the 65" Scattering Chamber for Long 120Flight-Path Measurements

e. The Y-ray Facility 120

f. Superconducting Solenoid Lens Electron Spectrometer 121

g. General-Purpose Beam Line 122

h. Nuclear Target Making and Development 123

ix

Page

III. THEORETICAL NUCLEAR PHYSICS 125

A. NUCLEAR FORCES AND SUBNUCLEON DEGREES OF FREEDOM 127

a. Three-Body Forces in Light Nuclei and Nuclear Matter 128

b. Present Status of the Nuclear Saturation Problem 130

c. Studies of Three-Body Forces and Isobar Degrees of 130Freedom in Nuclear Systems

d. Nucleon-Nucleon Potentials with Isobars 134

e. Consistency of Electromagnetic Current Operators and 136Relativistic Wave Functions

f. Relativistic Quantum Mechanics of Particles with 137Direct Interactions

g. Static Bag Source Meson Field Theory 137

h. Monte Carlo Method for Chiral Bag Models 138

B. VARIATIONAL CALCULATIONS OF FINITE MANY-BODY SYSTEMS 139

a. Ground States of Quantal Many-Body Systems 139

b. Monte-Carlo Variational Calculations of 4 He Droplets 140

c. '-shell Hypernuclei and A-nucleon Interactions 142

d. Alpha-Cluster Calculations of Be and Be 143

C. NUCLEAR SHELL THEORY AND NUCLEAR STRUCTURE 145

a. High Spin States in 91 Tc 145

b. The 6~ States in 2 8Si 145

c. Contribution of Giant Dipole State to Coulomb 146Excitation of 6Li and 7 Li

d. The Effect of the A(1236) on the g-facto:- of 147Nucleons

e. Beta Decay of 160(0+) to 16 N(0-) 147

f. Analysis of Inelastic Scattering of Pions 149

x

Page

D. INTERMEDIATE ENERGY PHYSICS 151

a. Phenomenological Many-Body Hamiltonian for Pions, 151Nucleons, and A Isobars

b. A Microscopic Study of A-Nucleus Dynamics 152

c. Absorption of Pions by the A = 3 Nuclei 155

d. Electroproduction of A from Light Nuclei 155

e. A Nonstatic DWIA Model for Pion Scattering 157

f. Production of Hypernuclei by Few GeV Electrons 157

g. A Model of Elastic and Inclusive P-Nucleus 159Scattering Above 500 MeV

E. HEAVY-ION INTERACTIONS 161

a. Analysis of 28Si + 28Si Scattering 161

b. Analysis of 1 60 and 180 Scattering from 54Fe 162

c. Extension of the CEOM Calculations 162

F. OTHER THEORETICAL PHYSICS 165

a. Angular Momentum near Solenoids and Monopoles 165

b. Triplet Correlations in Spin-Aligned Deuterium 165

IV. THE SUPERCONDUCTING LINAC 167

A. PROTOTYPE HEAVY-ION SUPERCONDUCTING LINAC 169

B. INVESTIGATIONS OF SUPERCONDUCTING-LINAC TECHNOLOGY 171

1. Superconducting Accelerating Structures 171

a. The ATLAS Resonator 171

b. Resonator Accelerating Field 173

c. Restoration of Performance 173

d. Slow-Tuner Controller 174

xi

Page

2. Time-of-Flight Technology 174

3. Superconducting Magnets 175

a. Prototype Bending Magnet 175

b. Heavy-Ion Beam Splitting 175

4. Near-Term Plans 176

C. THE ATLAS PROJECT 176

V. ACCELERATOR OPERATIONS 181

A. OPERATION OF THE TANDEM-LINAC ACCELERATOR 183

1. Operation of the Accelerator 183

2. Status of the Superconducting Linac 186

3. Linac Improvements 187

a. Resonators 187

b. Slow-Tuner Pressure Control 187

c. Liquid-Nitrogen Distribution 187

d. Helium Compressor 187

e. Energy-Measurement System 187

4. Upgrading of the Tandem 188

a. Computer Control and Monitoring of the Tandem 188

b. West Injector 188

c. Control of Tandem-Terminal Voltage 188

d. Focusing Lens in Terminal 189

e. Foil Stripping 189

5. Ion-Source Development 189

a. Ion-Source Test Facility 189

xii

Page

b. Inverted Sputter Source 190

c. West Injector for the Tandem 190

d. The SNICS Source 190

e. Hydrogen Loading 191

6. Near-Term Plans 191

a. Accelerator Operation 191

b. Linac Improvements 191

c. Tandem Improvements 192

d. Ion Sources 192

7. Assistance to Outside Users of the Superconducting 192Linac

a. Experiments Involving Outside Users 194

b. Outside Users and Institutional Affiliations 196

c. Summaries of Major User Programs 197

B. OPERATION OF THE DYNAMITRON FACILITY 203

1. Operational Experience 203

2. University Use of the Dynamitron 205

VI. DATA ACQUISITION AND ANALYSIS SYSTEMS 209

A. On Line 209

B. Off Line 209

C. Future 209

xiii

ATOMIC AND MOLECULAR PHYSICS RESEARCH

Introduction 211

VII. PHOTOIONIZATION-PHOTOELECTRON RESEARCH 213

a. Photoelectron Spectra of the Lanthanide Trihalides 214and their Interpretation

b. Photoelectron Spectra of Metal Oxide Vapors of Group 216III

c. Photoelectron Spectrum of B202 217

d. Photoelectron Spectrum of AiF 217

e. Photoelectron Spectra of BiX3 and BiX 218

f. Photoionization of Atomic Chlorine 218

g. UV-laser Photodissociation of Molecular Ions 220

VIII. HIGH-RESOLUTION LASER-rf SPECTROSCOPY WITH ATOMIC ANDMOLECULAR BEAMS 221

a. Hyperfine Structure of the Excited A 2n State of CaF 221

b. The Hyperfine Structure of Alkaline-Earth Monohalide 223Radicals: New Methods and New Results, 1980-1982

c. New Line Classifications in Ho I Based on High- 223Precision. hfs Measurements of Low Levels

d. Modification of Apparatus for Electric-Dipole Moment 224Measurement through the Stark Effect

IX. BEAM-FOIL RESEARCH AND COLLISION DYNAMICS OF HEAVY IONS 225

a. Lamb Shifts and Fine Structures of n = 2 Helium-like 225Ions

b. Precision Wavelength Measurements in Hlium 227

c. Position-Sensitive Detector for UV Spectroscopy 227

d. High-spin States in Neon 228

xiv

Page

e. Multicharged Tons at the Dynamitron 228

f. Measurement of the Transition Probability of 229Singlet-Triplet Intercombination Lines in Neon

g. Optical Measurements of Molecular-Ion Fragmentation 220

X. INTERACTIONS OF FAST ATOMIC AND MOLECULAR IONS WITH SOLID AND 231GASEOUS TARGETS

a. Contribution of Field-Ionized Rydberg Atoms to 232Convoy Electron Spectra

b. Microwave Field Ionization of Fast Rydberg Atoms 233

c. Coherent Stark States in Foil-Excited Fast Rydberg- 235

Atoms

d. Equilibration Lengths of K-Vacancy Production in 237Solids

e. Analysis of Molecular-Ion Stopping Power 237Measurements

XI. THEORETICAL ATOMIC PHYSICS 239

a. Transitions Between Quartet States of Three-Electron 241Ions

b. Influence of Increasing Nuclear Charge on the 241Rydberg- Spectra of Xe, Cs+ and Ba+

c. Collapse of the 4f Orbital for Xe-like Ions 241

d. Photoionization of the Inner 4d Shells for Xe-Like 242Ions

e. Energy Level Scheme and Transition Probabilities of 242Cl-like Ions

XII. ELECTRON SPECTROSCOPY WITH FAST ATOMIC AND MOLECULAR-ION 243BEAMS

a. Investigation of Rydberg- States Formed in Foil- 243Excited fast Ion Beams

xv

Page

b. InkLer-Shell Vacancy Fractions in Foil-Excited Ion 245Beams

c. Laser-Stimulated Ar L-Shell Excitation in Slow Ion- 245Atom Collisions

d. Simultaneous Laser- and Ion-Beam Excitation of a Na 248

Vapor Target

e. Further Investigations of the Formation of Rydberg 248States in Fast Ion Beams

f. Study of Li- and He-Autoionization as a Function of 248

Projectile Velocity and Charge State

g-. Auger-Electron Production Following- Ion Collisions 249in Solids

PUBLICATIONS FROM 1 APRIL 1982 TO 31 MARCH 1983 251

STAFF MEMBERS OF THE PHYSICS DIVISION 265

xvi

NUCLEAR PHYSICS RESEARCH

Introduction

The research program in nuclear physics in the Physics Division

spans a broad range of activities and contributes to many of the major

questions in the discipline. Activities may be roughly divided into three

broad categories. Research with the tandem-linac in heavy-ion physics is

doing well, though laboring under severe budgetary constraints, and outside

use of the facility has increased substantially. Progress on the

construction of the full ATLAS facility is coming along expeditiously and

it is expected to be completed on schedule in 1985. In medium-energy

physics, activities are continuing at LAMPF, as well as other accelerators,

though considerable effort was devoted this year to the preparation of a

proposal for a national electron accelerator facility. The medium-energy

experiments are concentrated (a) on understanding pion propagation and

absorption in nuclei, (b) studies of weak interactions and particularly a

neutrino-oscillation experiment at LAMPF, (c) studies of the two-ti..leon

system, and (d) some nuclear-structure experiments. The third major area

of activity is in nuclear theory where the role of sub-nucleonic degrees of

freedom .in.the nucleon-nucleon force and in nuclear matter are explored and

studies of the shell-model theory of nuclear structure are carried out, as

well as work on reaction theory in both the heavy-ion and the intermediate-

energy regime.

Some of the highlights of the past year are in the continued

improved operation of the superconducting linac, where outside user

-arfcipation has almost doubled to near 50% of the research.

The construction of ATLAS is proceeding well and there is every

reason to expect that it will come into operation on schedule.

Evidence has been found from gamma-ray studies for prolate-to-

oblate shapt changes in Dy isotopes.

Studies of fusion cross sections over a range of Ni - Sn isotopes

have revealed a striking- change (~ order of magnitude) over the 20% range

in neutron excess.

2

In medium-energy physics a survey of inclusive charge-exchange

(n no) reactions has been carried out over a variety of targets, showing

great sensitivity to the neutron excess. This complements the study of

inclusive pion inelastic scattering experiments done previously--

experiments which were fully analyzed and published during- the past year.

The importance of pion exchange currents in axial vector beta

decay has been conclusively demonstrated through studies of the 16N_ beta

decay.

A substantial proposal was prepared for a 4-GeV electron

microtron, GEM, which would serve as a major national center for the study

of electromagnetic interactions in nuclear physi s.

The role of the first non-nucleonic degree of freedom, the A, in

the nucleon-nucleon force, in the wave function of the three-nucleon

system, and in nuclear matter has been explored through theoretical

calculations.

A precision measurement was carried out of the branching ratio in

the decay of 7Be which refuted a recent experiment that could have led to

substantive changes in astrophysical calculations and had a direct bearing

on the solar neutrino problem.

3

I. MEDIUM-ENERGY PHYSICS RESEARCH

INTRODUCTION

The medium energy research in the Argonne Physics Division hasmade exciting progress in 1981--1982. Argonne experiments with pion beamsat LAMPF and TRIUMF have elucidated several new features of pion-nucleusinteractions. The dynamics of pion absorption in nuclei were explored intwo-nucleon-coincidence measurements and these experiments have already ledto a more complete understanding of the absorption process. Inclusivemeasurements of pion charge-exchange reactions have provided newinformation on the partition of the reaction strength and the isospin

dependence of the delta-nucleus optical potential. Nuclear structurestudies exploited the unique features of medium energy probes to examinethe response of the nuclear medium to spin-excitations which have a directbearing on the mean pionic field in the nucleus. Polarization measurementsin pion and electron induced reactions on the deuteron revealed substantialproblems in understanding the dynamics in this simplest nucleus. Studies

of the weak interaction have revealed new information on meson-exchangeprocesses and are testing- the fundamental structure of neutrinos in a

search for neutrino oscillations. Also of fundamental importance areexperiments to measure the electric dipole moment of the neutron and to

search for free quark trapping- at cryogenic temperatures.

The interaction of pions with nuclei has proven to be a rich,multifaceted area of study. Argonne measurements have demonstrated that

more than two nucleons erF involved in the pion absorption process and thishas led to the theoretical suggestion that more than one delta is formedwhen a pion is absorbed. A comprehensive series of measurements on He isunderway to examine the elementary absorption process on a T = 1 pair ofnucleons and the dynamics of three-body absorption. This holds importantconsequences for better understanding of pion absorption and of theinelasticities in the NuN phase shift parameters. New data on pon charge-exchange reactions complement previous charged-pion scattering- data anddifferences between the neutral and charged pion spectra are importantevidence for multi-step processes in pion scattering.

High resolution studies of inelastic pion scattering have focusedon spin-flip excitations which are currently the least-understood modes ofthe nuclear response. Measurements indicate that isoscalar and isovectorspin-flip strengths are quenched compared to theoretical expectations.Complementary measurements of proton and electron inelastic scatteringwhich will give a more complete characterization of these modes ofexcitation are in progress.

An understanding of the behavior of the few-nucleon systems isessential in describing the dynamics of complex nuclei. Measurements ofthe deuteron polarization in pion scattering- provide a central test ofmodels of pion absorption. These data also have important consequences inestablishing the existence of di-baryon resonances. Polarizationmeasurements in e-d scattering- have provided the first experimentalseparation of the deuteron charge and quadrople form factors at non-zeromomentum transfer. New measurements at higher energies will help revealthe nature of N-N interactions at short distances, <1 fm. Feasibilitystudies for a new experiment at an electron storage ring are in progress.

4

Weak interaction studies provide a direct look at thesubstructures of nuclei, since the underlying theoretical concepts areexpressed directly in terms of quarks, leptons, and gauge bosons.Fundamental characteristics of the weak interactions are being explored inexperiments studying neutrino oscillations, neutron beta decay, and theelectric dipole moment of the neutron. These experiments necessitate theconstruction of sophisticated detection apparatus. Low-energy weak-interaction studies are providing new information on meson exchangeprocesses and the induced pseudo-scaler coupling strength in nuclei.Despite a compelling theoretical framework, crucial ingredients in modernfield theories have not been observed as free particles. New high-precision searches are being carried out for quarks, magnetic monopoles andaxions.

5

A. STUDY OF PION REACTION MECHANISMS

Major efforts are in progress to characterize the interactions ofpions with nuclei in studies of the dynamics of the pion asorptionmechanism and pion scattering. The (Tr,NN) experiments on He are crucial

for a partial wave decomposition of the absorption process and can providefundamental information on the inelasticities of the nucleon-nucleon p ase-

shift parameters. Further measurements of 3-body absorption modes in He

and He will provide the basic structure to interpret the large number of

nucleons involved in the absorption process on heavier nuclei. Therelationship between inelastic scattering and absorption is probed ininclusive charge-exchange measurements, where experiments have determinedthe dependence of the distribution of reaction strength on the structure ofthe target. The comparison of these charge-exchange reactions withinclusive charged pion scattering data also provides new information onmultistep processes and the isospin dependence of the average isobarpotential.

a. Study of the Pion Absorption MEchanism in 3 He through the(nr,2p) and (Trpn) Reactions ('. Ashery, D. F. Geesaman,R. J. Holt, H. E. Jackson, S. M. Levenson,II J. P. Schiffer, J. R.Specht, E. Ungricht, B. Zeidman, R. C. Minehart,* R. R. Whitney,*G. Das,* R. Madey,t B. D. Anderson,t and J. Watsont)

In a previous study,' it was found that the (l~,pn) reaction

in 3 He and 4 He was suppressed by a factor of '30 compared with the (Tr+,2p)

reaction. This result indicates that pion absorption on a J=O, T=1 pair of

nucleons is strongly suppressed from that on a J=1, T=0 pair. If pion

absorption proceeds dominantly through the A-N orbital angular momentum L

= 0 or 2, then one would expect absorption on the T = 1 nucleon pair to be

strongly suppressed by conservation of spin and parity. However, a

theoretical calculation which includes the expected NA interaction, fails

to explain these data.

A measurement of the angular dependence of the 3 He(i~,pn)

reaction should provide information on the orbital angular momenta involved

in this process. These measurements are expected to begin in 1983 at

*

University oi Virginia, Charlottesville, Virginia.

tKent State University, Kent, Ohio.'Northwestern University, Evanston, Illinois.

1D. Ashery, R. J. Holt, H. E. Jackson, J. P. Schiffer, J. R. Specht, K.

E. Stephenson, R. D. McKeown, J. Ungar, R. E. Segel, and P. Zupranski,

Phys. Rev. Lett. 47, 895 (1982).

6

LAMPF. The proton-proton angular correlations from the 3He(n ,2p)p

reaction will be studied to determine the two-body ("quasideuteron") and

three-body absorption cross sections. For each detection angle of one

proton, the coincident proton will be detected over a large solid angle;

the measurement will be done for 5 detection angles. Proton-neutron

angular correlations from the 3He(n~,pn)n reaction will be studied to

determine two-body absorption in the 1S0 T = 1 proton pair.

The experiment will be performed in the P3 area utilizing the LAS

spectrometer and eight L0" x 10" x 4" plastic scintillators. The

measurements will be performed at 165, 245 and 315 MeV bombarding

energies. Auxiliary measurements of the 3 He(n+, r+p) and 3He(~,rrn)

reactions will be done at one energy and one pion scattering angle in order

to compare the relative momentum of a proton with respect to the p-n pair

and of a neutron with respect to the p-p pair in 3He. This is relevant for

the absorption measurement where the momentum of the absorbing pair with

respect to the third nucleon determines the width of the two-nucleon

angular correlation. The proposal was approved with high priority and will

be scheduled in 1983.

b. Study of Low-Energy Pion Absorption in 3He (A. Altman,*J. Alster,* K. Aniol,t D. Ashery, B. Barnett, t, D. R. Gill,t

W. Gyles,t R. R. Johnson,T S. M. Levenson,l J. Lichtenstadt,*M. A. Moinester,* R. Sobiev, R. Tacik,t and J. Vincent+)

The reactions 3He(n+,pp) and 3He(f~,pn) were studied at a pion

kinetic energy of TT = 65 MeV at TRIUMF. The 3 He nucleus is the simplest

system in which pion absorption on S = 1, T = 0 and S = 0, T = 1 nucleon

pairs can be studied and compared. Previous measurements of pion

absorption on the deuteron provided information only on the S = 1, T = 0

case at low density. The present 3He studies should help better understand

*Tel Aviv University, Israel.

tUniversity of British Columbia, Vancouver, B.C., Canada.

1TRIUMF, Vancouver, B.C. Canada.

University of Toronto, Canada.

Northwestern University, Evanston, Illinois

7

22003He (r+, 2P)

1800

1400-

':1000U)

S600-

V 3He (rK, pn)

b 60-

40

20

0* 40* 80* 120* 160*004op

F:g. I-1. The 3He(iPP) angular distributions are shown in the irNN center

of momentum. The solid lines are Legendre polynomial fits to the data.

8

the nucleon-nucleon interaction, the role of the A in pion absorption, and

the mechanisms of pion absorption in heavier nuclei. This 65-MeV

experiment is one of a series of planned experiments to be carried out at

165 MeV < T, < 300 MeV at LAMPF, using stopped pions and 110-Meg pions at

SIN, and at 25 MeV < TT < 85 MeV at TRIUMF. The ratio R = 3He+pn)(+3g

was found to be (3.4 .4)%. The n-3He+pn angular distribute show

significant asymmetry about 900 in the wNN rest frame as shown in

Fig. I-1. This implies a mixture of odd and even partial waves in the

final state which must be due to some ton-resonant [no A(1232) in the

intermediate state] contribution in the reaction mechanism.

c. Study of Pion Absorption Through the A(r,p)X Reactionat T. = 500 MeV (D. Ashery, R. J. Holt, H. E. Jackson,R. D. McKeown,* J. P. Schiffer, R. E. Segel,t K. E. Stephenson,and and J. R. Specht)

The angular dependence of inclusive proton spectra from (ir,p)

reactions on targets of 3He, 4He, C, Ni and Ta was measured for a pion

kinetic energy of Tn = 500 MeV. The data indicate that 3--5 nucleons

participate in the absorption process, a number similar to that observed in

Exp. 350 at pion energies near resonance.1 This is surprising since it

indicates that the number of nucleons involved in the absorption process is

independent of the 'IN + A coupling strength. In response to the earlier

ANL data, G. Brown et al.2 have recently suggested a novel model in which

absorption proceeds through the formation of two A's rather than one, i.e.

from an SU(4) quark model the n + 2N + AN + 2A process is favored over the

r + 2N + AN + 2N process. Since the two A's are then likely to decay by

involving two more nucleons, this model provides a natural explanation for

the absorption occurring on four nucleons. A manuscript describing the

data is in preparation.

*California Institute of Technology, Pasadena, California.

tNorthwestern University, Evanson, Illinois.

1 R. D. McKeown, S. J. Sanders, J. P.Schiffer, E'. E. Jackson, M. Paul, J.

R. Specht, E. J. Stephenson, R. P. Redwine, and R. E. Segel, Phys. Rev.

Lett. 44, 1033 (1980).

2G. E. Brown, H. Toki, W. Weise, and A. Wirzba, Phys. Lett. 118B, 39

(1982).

9

d. Survey of Inclusive Pion Scattering Near the Aq Resonance(E'. P. Colton, D. F. Geesaman, R. J. Holt, H. E. Jackson,S. M. Levenson,* J. P. Schiffer, J. R. Specht, K. E. Stephenson,B. Zeidman, R. E. Segel,* P. A. M. Gram,t and C. Goulding*)

A comprehensive series of measurements of inclusive pion

scattering from 4Hc, 1 2C, 58Ni and 20 8Pb with the LAS spectrometer have

been completed. Pion energy spectra were measured at 7 angles from 30* to

460 for the solid targets and at 5 angles from 300 to 1460 for the liquid

helium target. Complete data were obtained at n incident energies of 100,

160 and 220 MeV; more limited data were obtained on an H20 target at 100

MeV, on 12C at 300 MeV and on i~ scattering from 12C and 208Pb at 160 MeV.

Each pion energy spectrum i.s dominated by a large peak at an

energy near that corresponding to pions scattering from a free nucleon.

This indicates the importance of the quasifree reaction mechanism even in

the presence of strong pion absorption. Indeed, the spectra look rather

similar for each target and the angular distributions follow the

free n-nucleon angular distribution at back angles. At forward angles

however, the significant yield of low-energy pions cannot arise from the

quasifree mechanism and the yield in the quasifree peak is lower than that

expected from a free-nucleon-like angular distribution. These observations

signal the importance of higher-order processes and Pauli blocking effects

in the reaction mechanism.

The energy dependence of the distribution of reaction strength

for the n+ + 4He reaction is somewhat different from that observed on the

heavier targets as a consequence of the tight binding of the 4He nucleus.

Total inelastic scattering cross sections have been obtained for

each target by integrating the energy and angular distributions. The A

dependence of these cross sections is shown in Fig. [-2. Inelastic

*Northwestern University, Evanston, Illinois

tLos Alamos National Laboratory, Los Alamos, New Mexico.

'Florida A & M University, Tallahassee, Florida.

1D. Ashery, I. Navon, G. Azuelos, H. K. Walter, and F. Schleputz, Phys.

Rev. C 23, 2173 (1981).

10

100

3E

--()

.JW

500

100

500

500

IOO

50H. * PRESENT DATAo ASHERY et al.*0

I I

10A

. I

100

Fig. 1-2. The total inelastic cross sections are shown as a function of A.The solid lines are proportional to A- 4 . The open circles are fromthe results of Ref. 1.

1 1 1

T +=220MeV

&- 160 MeV

1 -

IOOMeV

opop

I I

11

scattering accounts for between 30% to 70% of the total reaction cross

sections for these nuclei.

This work has been completed with the submission of a

comprehensive paper presenting the results.

e. Inclusive Pion Charge-Exchange Reactions (D. Ashery,H. W. Baer,* J. D. Bowman,* M. D. Cooper,* J. Comuzzi,t A. Erel,*D. F. Geesaman, R. Chefetz,t R. J. Holt, H. E. Jackson,M. Leitch,*, R. P. Redwine,t R. E. Segel, J. R. Specht,K. E. Stephenson, D. R. Tieger,|I and P. Zupranski )

An experiment to study inclusive iF0 spectra from pion charge-

exchange reactions with 160-MeV wr was performed using the 'n0 spectrometer

at the LEP channel at LAMPF. This experiment is a continuation of our

studies of inclusive pion charge-exchange reactions which were previously

carried out at lower energies. The 7r0 spectra were measured at 0*, 400,

70*, 1100 and 1500 on targets of 12C, 1 4C, 58Ni, 12 0Sn and 20 8Pb. Analysis

of the measurements is under way. This experiment will establish the A

dependence of the total charge-exchange cross sections. A comparison of

the spectra of this experiment with those previously measured for inclusive

pion inelastic scattering provides an estimate of the importance of

multistep processes. Angular distributions for the energy-integrated cross

sections on 20 8Pb are shown in Fig. 1-3. The neutrL.i excess gives rise to

larger (g+ ,or0) cross sections by increasing the number of nucleons which

can participate in the (r+ ,ir ) reaction while increasing the inelastic

scattering and absorption channels which compete with charge exchange in

the (n~,r0) reaction. Furthermore, the quasifree mechanism is strongly

inhibited at very forward angles due to Pauli blocking.

*Los Alamos National Laboratory, Los Alamos, New Mexico.

tMassachusetts Institute of Technology, Cambridge, Massachusetts.


Northwestern University, Evanston, Illinois.

IlBoston University, Boston, Massachusetts.

I ' I8070

60

50

Pb (7r~,

rT)

I

Pb(7r+,

Jj

I I I I160*

Fig. 1-3. Angular distributions for inclusive (7r+, o) (circles) and (u~,1rO)(triangles) reactions of 160-MeV pions on 2 0 8 Pb.

12

I I' I

rT)

401

30

o20

E

Nb

-v i098765

4F-

I I0*

I I

40 800 1200

8ab

m m N m m or m

I

I I 1 1 1

13

f. Isospin Dependence of the 18, 160(Ir ,rro) Reactions(D. Ashery, H. W. Baer,* J. D. Bowman,* M. D. Cooper,*J. Comuzzi,t A. rzl,t D. F. Geesaman, R. Chefetz,* R. J. Holt,H. E. Jackson, M. Leitch,* R. P. Redwine,t R. E. Segel,J. R. Specht, K. E. Stephenson, D. R. Tieger, IIand P. Zupranski )

The inclusive differential cross sections for (Il ,nw") reactions

on 160 and 180 were measured at 160 MeV with the LAMPF 110 spectrometer.

This experiment was designed to study the isospin dependence of the partial

cross sections for inelastic scattering, charge exchange, and absorption.

Previous measurements of the inelastic scattering and the sum of charge

exchange + absorption show substantial differences in the distribution of

reaction strength on these two targets. By combining these data with

the 12C and 1 4C data described in the previous section, differing effects

of the valence nucleons being in the p shell or the s-d shell can be

identified

The (r+ , ro) cross section was found to be '30% larger on the T =

1 isotope than on the T = 0 isotope of each element while the (n~,n0 ) cross

section was '15% smaller on the T = 1 isotope. The (n+, no) energy spectra

on 160 are compared to (Tr,Tr') spectra in Fig. 1-4. The differences in

these spectra suggest that (r ,wo) reactions couple more weakly to the

absorption channel than do charged-pion inelastic scattering reactions.


tMassachusetts Institute of Technology, Cambridge, Massachusetts.


Northwestern University, Evanston, Illinois.

Boston University, Boston, Massachusetts.

1D. Ashery et al., Phys. Rev. Lett. 50, 482 (1983).

14

500 - -60 (7r+, M+')-

40 16 0(+,_o) -100

SXI -80300 - 30* '' i. .

(30*) i/, ~60200- $1 .- .*_ 40100 -; - 'X - -20

0 50050* -06 _

200U- (5*) -X 40 k

+ 100 - * -u-"- ..'-S20 k

80* * ~-60 S800200 (80)* t.f.

L 100 - -20

400 -rX 1 I0I0

W300 -A. (1080) 80 g - ' 60 C

-0 2 0 0 -. so- 440 -4 0

10 - -20

0c 0

0 1 I x I

0 50 100 150T.,,.( MeV)

Fig. I-4. Outgoing pion spectra from the l6O (+ ,+') reaction (C. H. Q.Ingram et al. to be published) at 163 MeV and the 160(nr+,Tro) reaction at160 MeV. The ratio of the scales is that of the corresponding pion-nucleon reactions. Angles in parentheses correspond to the (n+,,o)reaction. The lines are theoretical calculations [M. Thies, Nucl. Phys.A382, 434 (1982)] using the A-h model (solid lines) and the closureapproximation (dashed line).

15

g. Study of the (rr,rp) Reaction and Quasifree Scattering in 4 He(D. Ashery, D. F. Geesaman, R. J. Holt, H. E. Jackson, J. P.Schiffer, J. R. Specht, K. E. Stephenson, B. Zeidman, R. E. Segel,*and P. A. M. Gramt)

The measurement of inelastic pion scattering observed in

coicidence with a recoil proton was proposed for a target of 4 He. Angular

distributions will be obtained for n+ energies of 160, 220, and 350 MeV.

Emergent pions will be detected in the LAS spectrometer while an array of

scintillation counters that span a large solid angle will be used to detect

protons.

Data resulting from the coincident observation of pions and

recoil protons should provide a clear indication of the validity of the

impulse approximation in describing the scattering and of the importance of

contributions from higher order processes. The proposal was approved and

is expected to be scheduled in FY 1984.

*Northwestern University, Evanston, Illinois.


h. Measurement Near Threshold of 9Be(3He,7r) to the A = 12 IsobaricTriplet by Recoil Detection (R. D. Bent,* M. C. Green,* M. Hugi,*J. J. Kehayias,* P. Kienle,t H. J. Scheerer,t W. Schott,t andK. E. Rehm)

Study of composite-projectile pion production to discrete states

in the product nucleus can be extended close to threshold by using the

large solid-angle Indiana University Cyclotron Facility QQSP spectrometer

in conjunction with a heavy-ion focal-plane detector to obtain 4W detection

efficiency. In favorable cases, complete angular distribtions and total

cross sections for n~, r , and n+ production may be obtained simultaneously

with a single angle and magnetic field setting. We studied in a first

experiment the reaction 9 Be( 3 He, n) to the A = 12 isobaric triplet at E =

180 MeV. It was possible to identify 1 2 C and 1 2 B products in the focal

plane detector. The data are presently being analyzed by the Munich group.

*Indiana University Cyclotron Facility, Bloomington, Indiana.

tTechnical University, Munich, W. Germany

16

i. The A Dependence of the (e,e'p) Reaction in the QuasifreeRegion (D. F. Geesaman, W. S. Freeman, R. J. Holt,S. M. Levenson,* X. K. Maruyama,t R. E. Segel,* J. P. Schiffer,E. Ungricht, C. F. Williamson,* and B. Zeidman)

A proposal to study the A dependence of the (e,e'p) reaction at

q = 540 MeV/c at the Bates electron accelerator has been submitted. From

the A dependence of the ratio of (e,e'p) coincidence to (e,e') singles

events the mean free path of 140 f 20 MeV nucleons in nuclei will be

deduced. This information on the proton mean free path is essential for

the analysis of pion absorption phenomena and inclusive proton-induced

reactions. At the present time, proton elastic scattering data support a

long mean free path (--6 fm) while the inclusive proton data seem to require

a smaller value. The electron knockout reactions appear to be the cleanest

technique to provide macroscopic and microscopic measures of this

fundamental nuclear parameter.

*Northwestern University, Evanston, Illinois

tNational Bureau of Standards, Washington, D.C.

*Massachusetts Institute of Technology, Cambridge, Massachusetts.

17

B. NUCLEAR STRUCTURE STUDIES

Medium-energy probes can examine many new features of nuclearstructure due to the unique and differing selectivities of the Tr-nucleus,e-nucleus, and p-nucleus reactions. Measurements of pion inelasticscattering utilizing the EPICS system have established a quantitativeunderstanding of the pion-nucleus reaction mechanism. The isospinstructure of the pion-nuclear interaction can be used to separate neutronand proton transition amplitudes and makes pion scattering the ideal toolto study isoscalar and isovector spin-flip modes in nuclei. Theseexperiments have identified a systematic quenching of the isoscalar andisovector spin-flip strength to high-spin particle-hole states.Complementary data from proton and electron scattering reactions areimportant in establishing the underlying quenching mechanism. Otherexp iments have studied the momentum dependence of magnetic form factorsin Ca and searched for resonant structure in the four-neutron system.

a. Inelastic Scattering of Pions by 10B and 1 B (B. Zeidman,D. F. Geesaman, C. Olmer,* G. C. Morrison,t G. R. Burleson,*J. S. Greene,* C. L. Morris, R. L. Boudrie,R E. Segel, IL. W. Swenson, G. S. Blanpied,** B. R. Ritchie,** C. Harvey,ttand P. Zupranskill)

Elastic and inelastic scattering of n+ and ~ by targets of 10B

and "1B was studied at T, = 162 MeV. Angular distributions between 200 and

90* were measured in 50 steps for n+ and 7~. In addition, spectra were

obtained at 3 angles each at T, = 130 and 250 MeV, namely angles

corresponding to momentum transfers where the differential cross sections

for 2 = 2, 3, and 4 are maximized. For nuclei with T # 0 the isospin, the

energy dependence, and the angular distributions of the cross sections

allow multipole decompositions of mixed electric and magnetic transitions -

separately for neutrons and protons. Among the results are evidence, shown

in Fig. 1-5, for a rotational band built upon (lp 2 ,1d5 /2)4- neutron

particle-hole configurations. The transition to the 11/2+ state at 14.04

MeV excitation is found to be severely quenched. Preliminary results were

presented in a paper at the international conference in Amsterdam, 1982.

*Indiana University, Bloomington, Indiana.

tUniversity of Birmingham, Birmingham, England.

*New Mexico State University, Las Cruces, New Mexico.

Los Alamos National Laboratory, Los Alamos, New Mexico.

IlNorthwestern University, Evanston, Illinois.

Oregon State University, Corvallis, Oregon.

**University of South Carolina, Columbia, South Carolina.

ttUniversity of Texas, Austin, Texas.

18

7r100 4e . 2C

50 - 7.29MeV- I

20 ,

10 -

5-

2-

I-100- ,,9.19MeV

50 -/ . 9.27MeV -C

20 -/10 ,5:

50 4 1.29MeV

20-

10- -

5-

2-

I 14.,04 MeV20 -1/2)_

15- 1/

I0-8-6-

4-

0 40 800 1200

c.m.

5

0086

4030

00

5

080

60

40

0080

60

40

36

- -

. 4 .

.4 .

-

-il''

++ +++--

20a

15

1086

100

50

20

10

5

2

lo00-

50

20

10~

5

2

-a A --j4

7r +511111III

(5/2+)4

- 4 , e -

- -,

200150

1008060

4C30

10080

60

4030

'.,.(5/2+) 20-

0 (9/2+)-20

15 --00- -0-

8-

56

2 4

0* 400 800 120 120 2406c~m. INCIDENT PION

ENERGY (MeV)

7 +

- m -

-4

4-

3-

120 240INCIDENT PIONENERGY (MeV)

Fig. 1-5. Angular distributions and excitation functions at fixedmomentum transfer for inelastic pion scattering by 11B. The curves areDWIA calculations for T, = 162 MeV; the solid curves are based upon thenuclear structure calculations while the dashed curves include theadditional 4~ contributions to the cross sections that are deduced fromthe vi excitation functions.

(7/2f) -

/

/ +

-I ,

-

-o

b10

19

b. Inelastic Pion Scattering from 14N (D. F. Geesaman, C. Olmer,*B. Zeidman, G. C. Morrison,t G. S. Blanpied,* G. R. Burleson,*R. L. Boudrie, R. E. Segel, HR. E. Anderson,and L. W. SwensonI)

Elastic and inelastic scattering of 163-MeV pions from 14N was

studied with the EPICS spectrometer at LAMPF. CH2 N2 and CH2 targets were

employed at each angle, and the nitrogen spectra were constructed by

subtraction. Many 1 4N levels between 3 and 24 MeV were observed, but only

an upper limit could be set on the cross section for the 0+ T = 1 state at

2.31 MeV excitation. Angular distributions were obtained for 18 states.

The majority of the states are excited by L = 3 transitions. A state at

14.7 MeV appears to be a 5 state which is predicted by shell-model

calculations to be strongly excited in pion-inelastic scattering. Two

additional states, at 16.9- and 17.5-MeV excitation, may also be 5 states

and show some evidence of isospin mixing. Microscopic DWIA calculations

have, some success in describing the states observed. The project was

completed with the submission of a paper.

*Indiana University, Bloomington, IndLana.

tUniversity of Birmingham, Birmingham, England.


Los Alamos National Laboratory, Los Alamos, New Mexico.

IlNorthwestern University, Evanston, Illinois.


20

c. Excitation of 8 Particle-Hole States in 54Fe (B. Zeidman,D. F. Geesaman, R. D. Lawson, C. Olmer,* A. D. Bacher,*R. L. Boudrie,t C. L. Morris,t R. A. Lindgren,* G. R. Burleson,S. J. Greene, W. B. Cottingame, R. E. Segel, II L. W. Swenson,rand W. H. Kelly**)

The scattering of n+ and n~ by 54Fe was studied at T = 162 MeV

utilizing the EPICS system at LAMPF.' Particular interest was placed upon

the excitation of 8 states that result from particle-hole configurations

of the form (1f 7/2-1 ,1g 9 /2)8-. Since 54Fe has a neutron excess, both

isoscalar and isovector interactions contribute to excitation of T = 1

states while only the isovector interaction leads to T = 2 states. As a

result, different spectra are obtained from n+ and ir scattering. The data

are compared to theoretical nuclear structure predictions in Fig. 1-6.

Reasonable agreement can be obtained between the experimental results and

theoretical calculations if the isoscalar contributions are quenched by a

factor of ~2 relative to isovector contributions. The basis for this

quenching is under investigation.



*University of Massachusetts, Amherst, Massachusetts.

New Mexico State University, Las Cruces, New Mexico.

IINorthwestern University, Evanston, Illinois.


**Montana State University, Bozeman, Montana.

1 R. A. Lindgren et al., Phys. Rev. Lett. 42, 1524 (1979).

21

8-STATES IN 54Fe

-- THEORY

-----t EXPT.

(e ,el)

T T1TI II I

7r

IIT

11 - I ' ?i fI I

10

T1 II

8 10EXCITATION

T

I

_aaI s I '

12ENERGY

Fig. 1-6. Comparison of (e,c') M8 transition strengths and (ir,ir') peakcross sections (dashed lines) with theoretical calculations (thin lines).The calculations have been normalized to the yield for the 13.26-MeV T-2state. The heavy solid lines show the results of the calculations whenthe isoscalar transition strength is reduced by a factor of two. Thisreduction is required to obtain agreement with the pion inelasticscattering data.

0

0

C'

88

50

40

30

20 11IC

CU)

13

b-V

8

40-

30-

20-

10-

iiI

14

1

14(MeV)

01

IH-

50 -

40-

I

I

I

I

I

I

I

30-

201

io

I.i

f

10 12 14

I I

12

22

d. Isoscalar Quenching in the Excitation of 8 States in 52Cr(D. F. Geesaman, R. V. F. Janssens, B. Zeidman, G. C. Morrison,*R. L. Boudrie,t C. L. Morris,t G. R. Burleson,* S. J. Greene,*and L. W. Swenson )

A proposal has been submitted to LAMPF to use the EPICS system in

an investigation of the properties of 8~ states in 52Cr excited by the

scattering of 162-MeV rr+ and n~. Previous results for pion scattering

by 54Fe show that stretched transitions to 8 states with configurations

(f7% 2 g91 2)8- are observable with reasonable cross sections. The

experiment is directed toward answering a fundamental question concerning

"quenching" in inelastic scattering. The present experiment, in

conjunction with experiments utilizing other probes, should indicate

whether or not quenching of isoscalar transitions relative to isovector

transitions is merely an artifact of inadequate structure calculations or

requires a new quenching mechanism. In addition, information regarding the

absolute magnitude of the quenching should be obtained. This experiment

has been approved and is scheduled to run in 1983.

*University of Birmingham, Birmingham, England.




e. Excitation of 8 States in 52Cr (B. Zeidman, D. F. Geesaman,G. C. Morrison,* L. W. Fagg,t D. I. Sober,t X. K. Maruyama,*and R. A. Lindgren $

A proposal has been approved at NIKHEF-K, Amsterdam, for the

study of the inelastic scattering of electrons by 52Cr at 0lab - 1540 for

incident electron energies ranging from Ee = 140 MeV to Ee = 260 MeV, i.e.

q a 1.4 to 2.6 fm-1. Of particular interest are the 8~ states formed by

particle-hole excitations involving (1g9/2, 1f7/2 1)8- configurations. The

*University of Birmingham, Birmingham, England.

tCatholic University, Washington, D.C.

*National Bureau of Standards, Gaithersburg, Maryland.

University of Massachusetts, Amherst, Massachusetts.

23

identification of the 8 states, their locations and the transition

strengths will be compared to theoretical predictions and also utilized in

a study intended to ascertain the origins of quenching in both isovector

and isoscalar transitions. The experiment is scheduled to run in June

1983.

f. Polarized Proton Scattering from 26Mg (D. F. Geesaman,B. Zeidman, C. Olmer,* A. D. Bacher,* G. T. Emery,*C. W. Glover,* H. Nann, W P. Jones,* S. Y. van der Werf,tR. E. Segel,* and R. A. Lindgren )

We have measured the angular distributions and analyzing powers

for polarized proton scattering from 26Mg at 135-MeV incident energy at the

Indiana University Cyclotron Facility. A typical spectrum at 350

laboratory angle is shown in Fig. 1-7. Angular distributions were measured

in 50 steps from a laboratory angle of 100 to 600 for states in the

excitation energy range from 0 to 20 MeV. Five 6 states have been

identified based on the characteristic angular distributions of the cross

sections and analyzing powers.

This experiment is a continuation of our efforts to understand

the quenching of spin-flip strength in high-spin particle-hole states. The

phenomena are now well established throughout the periodic table for AT = 1

transitions, and are also observed for AT = 0 transitions in pion and

proton scattering. By studying the inelastic strength as a function of

deformation in the s-d shell, and as a function of angular momentum

transfer, we hope to distinguish between several proposed explanations for

the quenching mechanism, including the possiblity of isobar-hole admixtures

in the nuclear wave functions.


tK.V.I., Groningen, The Netherlands.


University of Massachusetts, Amherst, Massachusetts.

24

.....................................,........ ~ 111 UUUI1 11111 wIDE,~vm

10 15EXCITATION ENERGY (MeV)

Fig. 1-7. A proton spectrum at 350 resulting from the scattering of

135-MeV spin-up protons by 26Mg. This spectrum is a composite of the

data obtained with three field settings of the QDDM spectrometer.

10000

8000-

6000F--JW

I- I ITIT

2 6 mg (''p')

SPIN UPo =350

pII

40001

2000H-

Cl5 20

III-" lilall AIIII IIAll IIIII

TTT1ITrvv vm

TT -IfI

! 1 _ l = i r1 1 f S a m s1 l 1 1 1 1 1 1 l 1 l l 1 1 1 1 1 1II.mblail_ rr Pik i i l 11 11

. i 1I " rvIIIIIIIIIIII191111111 .. r

i

25

g. Transverse Electron Scattering by 26Mg (A. D. Bacher,*D. F. Geesaman, R. S. Hicks,t R. L. Huffman,t R. A. Lindgren,tX. K. Maruyama,* C. Olmer,* M. A. Plum,t and B. H. Wildenthal )

The inelastic scattering of electrons by 2 6Mg was studied using

the 1800 inelastic electron scattering facility at the Bates Linear

Accelerator Laboratory. Initial' preliminary measurements were made at

incident energies of 140 and 192 MeV where the momentum transfer

corresponds to the peak of the transverse form factors for E4 and M6

multipolarities, respectively. Five 6 states were tentatively identified

including the 6~, T = 2 state at 18-MeV excitation. These data along with

that of the previous (p,p') measurement will permit the determination of

the isoscalar and isovector spin-flip strengths for each 6 state. Final

data for this experiment are expected to be taken in early FY 1983.


tUniversity of Massachusetts, Amherst, Massachusetts.

*National Bureau of Standards, Washington, D.C.

Michigan State University, East Lansing, Michigan.

h. Inelastic Scattering of p + 4 8Ca at 160 MeV (K. E. Rehm,R. E. Segel,* P. Kienle,t D. W. Miller,* and J. R. Comfort )

The investigation of possible mesonic effects on inelastic proton

scattering to the 10.24-MeV 1+ state in 48Ca was completed and the results

have been published.' Cross sections and analyzing powers for low lying

states up to Ex = 9.4 MeV have been extracted. Angular distributions and

analyzing powers for some of the states are shown in Fig. 1-8. Of

particular interest are unnatural parity states (4-) between 5--7 MeV and

some high spin states around Ex = 9 MeV. DWIA calculations for these

states are presently being performed.


tTechnical University, Munich, W. Germany.

*Indiana University Cyclotron Facility, Bloomington, Indiana.

University of Arizona, Tucson, Arizona.

1K. E. Rehm et al., Phys. Lett. 114B, 15 (1982).

26

I I I I

48Ca (p, p )C48Ca

EIb=I59.8MeV _

I

104

13I0

2102

I00

,*6.342MeV

0e0 (4+)0.00%.

0000

1I

- .. .0 -

0 0 :

5.729MeV -(5~)I-

I __I I I I

500

1.0

C

0.51-

o

a 0.5

0

0.5

o

-0.5

I.'U I

-0.5

-1.010 200 30 40

c.m.

48 -6.(Ca ,1489

C(p, p) CElab=159.8 MeV

00" 0

- "* . ELASTIC* ." -

. *0 .

4* 3.832MeV

+ (2+)

0.,Do

40

1 00

4.507 MeV(3-)

*. ! 0

. SO* 0

6.342 MeV -4 + (4+)

t * * 9.9

"5,

"t01

t *-S*. 5.729 MeV*. (5-)

__I I I 1 I I 1

100 200 30' 4Q0 50 600 70

c.m.

Fig. 1-8. Angular distributions and analyzing powers for low-lying states

in 4 8Ca populated by inelastic n-scattering at ELab = 160 MeV.

000.

.

0e

"1

"

-0

-0

0

0

. ELAST I C

" 0

* * "*.3.832MeV

S . 0 (2 )

* 0

0 0

.0 " "*.... (3)-

U)

E

b

00

10

1O

I0

-

.

""0

w

I

i

-

:-

V

r

I

27/a

i. Study of the 4He(Tr~, n+) Reaction at Small Angles(D. F. Geesaman, S. J. Greene,* R. J. Holt, R. D. McKeown,tC. L. Morris,* J. R. Specht, K. E. Stephenson, J. Ungar,tand B. Zeidman)

A search for structure in the 4n system via the 4He(rr~,Tr+)4n

reaction in the energy range 130--200 MeV was undertaken. The Argonne

Large Acceptance Spectrometer (LAS) was used to detect T+ emerging from a

liquid helium target located slightly upstream of the usual LAS target

position. A 12" diameter circular dipole centered over the pivot deflected

positive pions at 00 toward LAS while deflecting the negative pions from

the P3 beam away from the spectrometer. The efficiency and resolution of

the system were determined by measurements of 12C( ~,T+) double-charge

exchange. Analysis of the data does not reveal any statistically

significant structure in the spectra. An upper limit for the 00 cross

section for the formation of the tetra-neutron is 7 15 nb/sr which is

approximately 2 orders of magnitude lower than previous results.


tCalifornia Institute of Technology, Pasadena, California.


j. Discrete States from Pion Double-Charge-Exchange onHeavy Nuclei (D. F. Geesaman, R. J. Holt, J. R. Specht,

and B. Zeidman)

Eikonal model predictions for analog-state transitions in pion

double-charge-exchange (r+ ,r~) suggest that 00 cross sections for heavy

nuclei should be large and comparable to those for very light nuclei. Near

resonance, cross sections for nonanalog transitions are expected to be

roughly equal to those of analog transitions. The LAS spectrometer,

together with a circular sweeping magnet, will be used to test these

conjectures. A P3 channel failure forced postponement of this experiment

which, because of its relatively short duration, will be rescheduled in

conjunction with another DCE experiment that utilizes LAS.

29

C. TWO-NUCLEON PHYSICS WITH PIONS AND ELECTRONS

After years of effort, an understanding of the N-N interactionremains a central concern for nuclear physics. Measurements ofpolarization observables in pion and electron reactions on the deuteronprovide information on the pion absorption mechanism and on isoscalarexchange currents. The data on the angular distribution of the tensorpolarization in Tr-d scattering cannot be explained by any current theory.During 1982 the tensor polarization t20 in e-d elastic scattering wasmeasured foj the first time. Since the momentum transfer range(1.7--2 fm ) of this measurement is comparable with that of the tensorpolarization measurements in n-d scattering and since good agreement wasfound between the results and calculations which employ reasonable deuteronwave functions, this confirms the suspicion that the discrepancies betweenthe experiment and calculations in n-d scattering arise from an incompleteknowledge of the inelastic channel (nd + NN) rather than of the deuteronwave function.

Studies to continue these measurements at higher momentumtransfer using an electron storage ring are underway. In otherexperiments, low-energy photodisintegration measurements revealed problemswith the conventional nucleon-meson descriptions of the deuteron in

predicting the neutron polarization in the d(y,n) reaction.

a. Energy and Angular Dependence of Tensor Polarizationin Pion-Deuteron Elastic Scattering (R. J. Holt, W. S. Freeman,D. F. Geesaman, J. R. Specht, E. Ungricht, B. Zeidman,E. J. Stephenson,* J. D. Moses,t M. Farkhondeh,* S. Gilad,and R. P. Redwine )

Recent theoretical calculations have shown that the tensor

polarization t2 0 in n-d elastic scattering is sensitive to true pion

absorption and the possible existence of dibaryon resonances. Our previous

measurements of the angular dependence of t20 at T. = 142 MeV do not agree

with the results of present three-body calculations. This indicates that

pion absorption on two bodies is more complicated than previously believed

or there is an effect from dibaryon resonances.

Since a possible resonance effect was suspected, it was decided

to determine both the energy and angular dependence of t2 0 . An experiment



*Graduate Student, Massachusetts Institute of Technology,

Cambridge, Massachusetts.

Massachusetts Institute of Technology, Cambridge, Massachusetts.

30

is presently in progress which should provide measurements of the angular

distribution of t20 at 180 and 256 MeV. (In fact, the measurement at 180

MeV is now complete and the data analysis is in progress.) This work

should be completed in 1983.

In response to some recent results from a SIN group, we have

checked the energy dependence between T, = 134 and 151. MeV of t 2 0 at 6d =

18.00. We observed no remarkable energy dependence over this small energy

range. The results of a preliminary analysis agree with our previous

measurement at 142 MeV and we conclude that the SIN data are probably

erroneous.

b. Tensor Polarization in Electron-Deuteron Elastic Scattering(R. J. Holt, J. R. Specht, K. E. Stephenson, B. Zeidman,E. J. Stephenson,* J. D. Moses,t D. Beck,M. Farkhondeh, S. Gilad,* S. Kowalski,* R. P. Redwine,*M. Schulze, W. Turchinetz,* M. Leitch, and R. Goloskie**)

During 1982 the tensor polarization t2 0 in e-d elastic scattering

was measured for the first time. The tensor polarization is dominated by

the charge and quadrupole form factors of the deuteron, and consequently,

it is sensitive to the tensor part of the deuteron wave function and at

high momentum transfer the short-range part of the wave function. The

deuteron tensor polarimeter that was developed in order to measure t2 0 in

n-d scattering was employed at Bates in order to measure the

polarization. The results indicate that the data are in good agreement

with theoretical calculations that use reasonable deuteron wave

functions. In Fig. 1-9, the present work is compared with predictions) of

t20 of the Paris model, both with and without meson exchange current




TRIUMF, Vancouver, British Columbia, Canada.

Graduate Student, Massachusetts Institute of Technology, Cambridge,

Massachusetts.

**Worcester Polytechnical Institute, Worcester, Massachusetts.

1M. I. Haftel et al., Phys. Rev. C 22, 1285 (1980).

31

0

2 2H(e,e) H

-0.5

t2t20 PA RIS

-I.0-PRESENTWORK

PARIS (MEC)---

-1.50 5 10 15

2 -2q(fm )

Fig. I-9. Comparison of present measurements of t2 0 in e-d elasticscattering with the predictions of the Paris potential with andwithout meson exchange current corrections.

32

corrections, for the deuteron. The agreement with these models is

remarkably good. Cleary, in order to study the meson exchange current

effect one would need either higher accuracy at the low momentum transfer

or push the measurements of t20 to higher momentum transfer. The tensor

polarization was measured for two values of momentum transfer: q = 1.75 and

2.0 fm~l. Since this momentum transfer range is comparable with that of

the tensor polarization measurements in Tr-d scattering, then this indicates

that the discrepancies between the experiment and the calculations in Tr-d

scattering arise from an incomplete knowledge of the inelastic channel (ird

+ NN) rather than that of the deuteron wave function. The results indicate

that it will be somewhat difficult to extend the measurements to higher

momentum transfer even after the energy doubler at Bates becomes

operational. Thus, we are investigating alternative options, such as the

use of a tensor polarized target in an electron storage ring.

c. Feasibility Study of Electron Scattering Experiments with aTensor Polarized Deuterium Target in an Electron Storage Ring(R. J. Holt, L. S. Goodman, J. R. Specht, E. Ungricht,B. Zeidman, J. D. Moses*)

This study is centered around the Aladdin storage ring at

Wisconsin. This ring is expected to be operational in 1983 and is expected

to produce a 1-GeV electron beam with a circulating current of J00mA. In

an experiment of this type baffles will be necessary to localize the target

and to provide differential vacuum pumping. A movable baffle has been

designed and constructed for the ring. This baffle will be employed in

order to study the radiation background, transverse "tails" associated with

the beam and the interaction of the beam in the presence of a baffle. If

this part of the experiment proves feasible, then construction of a tensor

polarized atomic deuterium target would begin in 1983 or 1984.


33

d. Deuteron Tensor Polarimeter Development (R. J. Holt,E. J. Stephenson,* M. Farkhondeh,t and M. Schulzet)

In order to simplify the high-q measurement of t2 0 in e-d

scattering at Bates, a deuteron tensor polarimeter which has a higher

operating energy and figure-of-merit than those of the existing polarimeter

would be necessary. A search for a suitable reaction was carried out with

the 80-MeV, tensor-polarized deuteron beam available at the Indiana

University Cyclotron Facility. Deuteron elastic scattering and reactions

were studied for 3,4He, 6,7Li, 9Be and 12C. Thus far, no reaction was

found which would lead to an improvement over the existing polarimeter. At

present, the only reaction which offers any hope of improvement is d-p

elastic scattering. It is expected that the cross section and analyzing

power of this reaction will be measured during 1983.


tGraduate students, Massachusetts Institute of Technology, Cambridge,

Massachusetts.

e. Photoneutron Physics (R. E. Holland, R. J. Holt, H. E. Jackson,R. D. McKeown,.J. R. Specht, and K. E. Stephenson)

The end of 1982 marked the completion of a long series of

photoneutron studies at Argonne. The photoneutron facility has been placed

in a standby mode. During the past year, the photoneutron program centered

around photodisintegration studies of the deuteron. High accuracy

photoneutron polarization and relative angular distribution measurements

were performed in the photon energy range of 5--19 MeV. The angular

distribution for the D(Y,n) reaction is sensitive to E1-E2 amplitudes,

while that for the photoneutron polarization is sensitive to El-M1

interference. It was found that the angular distributions are in

disagreement with the theoretical calculations by 5--15%. This indicates

that the multipole composition of even the simplest photodisintegration

process is not completely understood.

The measurements of photoneutron polarization at a reaction angle

of 90* formally depend on El-M1 and E1-E2 interference terms. However, all

calculations show essentially no dependence on the El-E2 amplitudes. Thus,

34

one would expect the polarization to be sensitive through the M1 amplitude

to meson exchange currents in the deuteron. The trend of the data indicate

possible agreement with the calculation at low energy EY 7.0 MeV, but

clear disagreement at higher energy, ~12.0 ftV. The effect of including

meson exchange currents1 in the theory is to produce an even greater

disagreement between the present results and the calculations.

Although the theories also originally failed to explain the

photodisintegration cross section at 00, an earlier discrepancy, that

disagreement occurred at much higher energies and is now believed to be

explained by relativistic effects. The present work is more surprising

since many effects such as relativity, nucleon form factors, details of the

deuteron wave function and uncertainties in the final-state interactions

are not important at such low energies.

Measurements of the photoneutron polarization at 1350 were also

performed and analysis of the data is in progress.

1E. Hadjimichael, Phys. Lett. 46B, 147 (1973).

35

D. WEAK INTERACTIONS

The goals of the weak-interaction program are to attempt todetermine the structure of weak currents, and to use weak interactions as aprobe of hadronic currents. A search for neutrino oscillations at LAMPFaddresses two central issues in gauge theories of weak interactions, themass and the flavor purity of neutrinos. Argonne has assumed a majorresponsibility in the construction of a large and sophisticated neutrinodetector for this experiment. Low-energy source and accelerator-basedexperiments provide tests of right-handed currents, the conserved vectorcurrent hypothesis and the existence of second-class currents. Theimportance of pion exchange currents in pseu g-scalar bqa deays has beenconclusively demonstrated in studies of the N, 0 to 0, 0 betadecay. This provides a measure of the induced pseudo-scalar coupling-constant for A = 16 of gp = 11 2, close to the free nucleon value of7.0 + 1.5.

a. Neutrino Oscillations at LAMPF (J. Donohue,* S. J. Freedman,C. A. Gagliardi,t G. T. Garvey, L. Hyman,* R. Imlay,M. Kroupa,NU T. Y. Ling, R. D. McKeown,** W. Metcalf,B. Musgrave,* J. Napolitano, T. Romanowski, F and M. Timko )

The possibility and consequences of V oscillations have recently

received much attention because of developments in the extension of gauge

theories to include strong and electroweak interactions. These new Grand

Unified Theories (GUTS) rather naturally produce massive V's and flavor

mixing in the lepton sector among- other striking- predictions. We are part

of a collaboration which has an approved experiment (E645) at Los Alamos

Meson Physics Facility to search for V oscillations. The neutrino source

is to be the LAMPF beam dump which yields Ve, vu and vu neutrinos from

stopped pion and muon decays.

The energies of the V's produced are such that only Ve or ve can

be detected via charge-changing interactions. Two kinds of oscillation

experiments are to be performed. In one the disappearance of electron


tTexas A & M University, College Station, Texas.

*High Energy Physics Division, ANL.

Louisiana State University, Baton Rouge, Louisiana.

1Thesis Student, University of Chicago, Chicago, Illinois.

Ohio State University, Columbus, Ohio.

**California Institute of Technology, Pasadena, California.

36

neutrinos will be measured by observing the spatial dependence of the

neutrino flux with the reaction (Ve + d) + (e + 2p). The other phase of

this experiment involves the appearance of Ve neutrinos via v + e; the

Ve being detected via ( , + p) + (e+ + n). The latter experiment is the

one being pursued first.

A crucial aspect of this experiment is that it must be able to

reject backgrounds with an efficiency greater than 1-10~7. Argonne has

accepted the responsibility of prototyping, designing, and implementing a

shield to reject backgrounds due to either charged or neutral cosmic

rays. The Physics Division has designed and tested a prototype active

shield for charged cosmic rays. This prototype is a tank of liquid

scintillator with an active volume of 1.5 m x 1.5 m x 15 cm viewed by four

five-inch diameter hemispherical photomultiplier tubes. (See Fig. I-10 for

sc'iematics). Tests of this detector have shown it to be excellently suited

for the task. A typical pulse-height spectrum is shown in Fig. I-ll.We

have drafted a paper on these tests and will submit it to Nuclear

Instruments and Methods.

We are now studying backgrounds due to the neutral component of

cosmic rays. At present, these tests consist of measurements of the energy

deposited in a 10" dia x 10" long NaI(TZ) crystal which do not deposit

significant energy in a plastic scintillator anticoincidence shield

surrounding the crystal. Preliminary results seem to be consistent with

cosmic-ray neutrons, and with bremsstrahlung from the electrons resulting

from muon decays. This effort is continuing.

b. Beta Decay of Polarized Nuclei and the Decay Asymmetry of 8Li(R. Bigelow,* S. J. Freedman, G. Masson,* J. Napolitano,and P. Quin*)

Using the FN Tandem facility at the University of Wisconsin-

Madison and the accompanying polarized ion source, we have begun a program

of studying the weak interaction via the beta decay of polarized nuclei.

Such a study yields information on the validity of CVC, the existence of

second-class currents, and the magnitude of certain nuclear matrix

elements.

*University of Wisconsin, Madison, Wisconsin.

PLAN

A)

FILL PORT

D

0LED

EB')

RUBBER PAD

RETAINING HAMMAMATSURING R1391

FLANGE

VITON 0-RING

CPTUCL NGLUCITE WINDOWCOUPLINGGREASE

ELEVATIONS

I.5m

Fig. I-10. Schematic of the liquid-scintillator-active-shield prototype and hemispherical phototubemounting arrangement. There are four such phototube assemblies on the prototype at locations markedA, B, C, and D. The prototype was studied in a self-triggered mode and with a cosmic-ray telescopeover regions 1, 2 and 3.

E

38

- I ' ' ' ' I ' ' ' - j ' ' ' ' i' ' ' ' -

1000

Cl)

zW 10 0

U--

0

w 10m

z

0 200 400 600 800 1000

PULSE HEIGHT (channels)

Fig. I-11. A pulse-height spectrum from one of the phototubes triggeredon the cosmic-ray telescope. Loose cuts have been made on the telescopedata to eliminate non-single-particle triggers. Tests with the LEDshow that this spectrum corresponds to approximately 1000 photoelectronsemitted on average from the photo cathode.

39

We are presently studying the beta decay of polarized 8Li,

produced with a polarized deuteron beam on a cold target of 7Li metal kept

in a magnetic holding field. The asymmetry between up and down

polarization states is detected by two electron-detection telescopes.

Total electron energy is measured in large plastic scintillators. This

investigation will therefore yield the energy dependence of the decay

asymmetry. Data from our first run are being evaluated and the detector is

being refined.

c. A Test of V-A Positron Decay (S. J. Freedman, G. T. Garvey,J. Napolitano and A. Rich*)

We are considering a possible experiment to measure the helicity

of positrons from nuclear positron decays as a sensitive test for the

presence of V + A currents. The experiment would utilize a novel and very

sensitive polarimeter for positron helicities developed by A. Rich and co-

workers at Michigan. The method utilizes the spin dependence of

positronium annihilation in a magnetic field as a measure of the positron

spin. A possible experiment would require intense sources of 2 6Alm and 30P

that could be produced either at the Dynamitron or the Argonne Cyclotron.

A feasibility study is currently underway.

*University of Michigan, Ann Arbor, Michigan.

d. The Beta Decay Rate of 1 6 N(J1T = 0-, 120 keV); Meson ExchangeCurrents and the Induced Pseudoscalar Coupling Constant(C. A. Gagliardi, G. T. Garvey, S. J. Freedman, and J. R. Wrobel)

We have improved (by a factor 2) our previous measurement of this

important decay. The bulk of the error in the 0~ beta decay rate now rests

with the uncertainty in the decay rate of the Jn = 2 16N ground state

which is under investigation. Apart from this error, currently at 11%, we

have reduced all other sources of error in this decay branch to 4%. The

improvements in the measurement over our earlier result involve higher

statistics and more uniform targets.

40

The 0 + 0+ decay rate is important for quantifying the role of

pions in the nuclear medium. A pseudoscalar transition such as this one is

believed to be effected strongly by the presence of pions in nuclei. Their

strong effect on this transition is just a consequence of the time-like

component of the axial vector current. Sizable meson exchange effects have

long been predicted and detailed calculations have recently been carried

out for the 16N 0 + 0+ case. Thus this particular measurement is

significant as it represents a case where the nuclear structure is both

simple and calculable and the N capture rate between the 160 ground state

and the 16N,JE - 0 120-keV level is well known (Au = 1560 94 sec-).

This ratio of the V capture rate to the beta decay rate is very sensitive

to the pion currents and insensitive to the details of nuclear structure.

Figure 1-12 shows the comparison of theory to the measured decay

probability (Au) along with our measured value of the beta decay

probability (As).

The difficulty in measuring the beta decay rate arises from the

fact that it is a weak decay of an excited state with an electromagnetic

decay rate of AY = 1.32 0.02 x 105 sec-1 . Thus the beta decay branch is

the order of 10-6 of the total decay probability for this level. Using

techniques described in last year's submission we have measured A8 = 0.45 t

0.05 sec-1 . Figure 1-13 shows the beta rate measured as function of time

with respect to a peak burst over an 18-hour run. As stated in the opening

paragraph of this section the bulk of the error lies in the 16N ground

state to 160 ground state decay branch which is used to calibrate the

efficiency of our beta detector system. This work has led to two invited

talks and a Physical Review Letter. A more detailed Physical Review

article is nearing completion.

e. 0+ + 0~ Beta Decay of 1 6 C Ground State (C. A. Gagliardi,G. T. Garvey, N. Jarmie,* and R. G. H. Robertson*)

As part of the effort to establish the role of virtual pions in

nuclei we have measured the beta decay of the 1 6 C ground state to the 0~,

120-keV level of 16N. These pseudoscalar matrix elements are known to be


41

9P/9A

2

)13

CO

'0

0o 0.2 0.4

A (secs)

Fig. 1-12. Calculation of Towner and Khanna, Nucl. Phys. A372, 331 (1982)compared to experimental value for A and As. The open points are theresult of impulse approximation calculations while the closed pointsinclude meson-exchange currents. Curves are shown for 3 values of

gp/g A"

42

200

160

-

1201

401

OL0

' I

I I I II I

10 20I I I I I I

30 40TIME (psec)

50

Fig. 1-13. The rate as function of time observed in the beta telescope.

The smooth curve is a fit to an exponential (T = 7.8 0.7 ps) plus

a constant background.

(!1F-z

0

60

-4

2 1

I I

I I ' I

I -- TT

J

4 i,141 11 lill. 4i I v TITTiTliT l7fij

801

i

43

' I

-Ssii.".s.

0

S00

0

(a)

"".0

000

00

0 000

12-

.e' 09 g~*"0

I I

250 270I I

-u I I I

I (b)

- " , -

3

4mo *" af * 0

H4

*00

1 l I290 590CHANNEL NUMBER

610 630

Fig. 1-14. The gamma-ray pulse-height spectrum in the region of the120-keV line for 3 different time intervals. The top spectrum isfrom the first time bin. The middle spectrum is taken 0.88 sec. laterand the bottom spectrum is taken 1.94 sec. later. Note 160 has a0.75-sec. half life.

15x103

12

9

12

xl03

C,)F-zD0

61

-13

'2

- -I JI I I T -T -

I I i I II I

44

greatly affected by pion exchange currents and further the transition

matrix elements are very similar to those required to produce AT = 1 parity

mixing in hadronic systems. This experiment represents the first time that

the 0~ branch has been observed in the decay of 16C. The measurement was

carried out at the LANL Tandem Van de Graaff, where 16C was produced via

the 14C(t,p)16C reaction at Et = 6.0 MeV. The use of both a radioactive

beam and target allowed the preparation of a much cleaner and stronger 16C

source than had heretofore been possible. The prominent decay modes of

the 16C ground state are to JTF = 1+ neutron unstable states in 1 6 N. We

detected the neutrons with a stilbene crystal, the betas in a thin (0.8 mm)

plastic scintillator and photons in a 12.5 cm3 Ge(Li) detector. The

absolute efficiency of the Ge(Li) was fixed with calibrated sources while

the beta counter efficiency was determined at ANL using - Y coincidences

in the 20F + 20Ne decay. Our results for the 16C decays are a branching

ratio of 6.8+0' x 10-3 for the decay to the 0 state and a limit of <10-3

for the branch to the 1 state. Figure 1-14 shows the Y-ray energy

spectrum as a function of time in which the branch to the 0~, 120-keV line

is clear.

As this 0+ + 0~ decay depends principally on 21/2 + 1P1/2

transitions the rate depends on the amount of the (2S /2) component in

the 16C ground state. Using an estimate of this component by D. Kurath and

our earlier value for the 16N(0~) + 160 ground-state decay rate, we predict

a value of the 0+ + 0- branch that is 2.5 times what we observed. A proper

calculation of the nuclear structure must be done to determine if we have

achieved a quantitative characterization of these pseudoscalar transitions.

f. The Branching Ratio to the 160 Ground State for the 16N Ground State(A. Heath and G. T. Garvey)

The branching ratio for 16N ground-state decay to the 160 ground

state and 6.13-MeV level are 26 2% and 68 2%, respectively.

Unfortunately, the errors in these determinations are highly correlated so

that the ratio of these branches is 26 2/68+2 = .385 * .040. This

uncertainty is responsible for the bulk of the 11.5% error in our recent

measurement of the beta decay rate of the 1 6 N J= - 0~, 120-keV level as it

entered into the calibration of the beta detector efficiency. Reducing the

45

error in the above ratio to 5% would reduce the error in the 0~ branch to

6.9%.

The measurement of the 1 6N ground-state decay is being carried

out at the Dynamitron using the 15N(d,p)16N reaction at Ed = 1.7 MeV. The

beta rays are being measured in our flat-field beta spectrometer. The

absolute acceptance of the spectrometer is being measured employing --Ycoincidences in the decay of 20F made via 1 9 F(d,p) 2 0 F. We expect to be

able to calibrate the absolute efficiency of this spectrometer to 3--4%

thereby being able to measure the 16N branching ratio to an acceptable

level. This device will also be employed to measure the beta spectra

associated with the fission of 2 55Cf, an experiment which bears on the

questions of Y spectra associated with heavy fissioning nuclei (U2 35).

g. Neutron Beta Decay (S. J. Freedman, D. Dubbers,* Y. Last,*P. Bopp,* H. Schatze,* and 0. Schrpft)

Neutron beta decay represents a unique opportunity to study the

semileptonic weak interaction in a tractable hadronic system. The first

run of a new-generation neutron beta decay experiment was conducted in 1982

at the Institut Laue-Langevin reactor by a collaboration consisting of

scientists from Argonne, Heidelberg, and the ILL. The experimental goals

are to provide a new high-precision value for the average reaction

asymmetry parameter A, a test of the conserved vector current hypothesis

through a measurement of the energy dependence of A, and a value for the

neutron lifetime (at the 1% level) by a new experimental method.

The experimental instrument consists of a ̂ 2m long

superconducting solenoidal spectrometer equipped with two scintillation

detectors. A novel geometry allows us to observe polarized neutron decay

over a large region and thus along with the high flux polarized beam at the

ILL, the resulting count rates are more than two orders of magnitude higher

than previous experiments. The first run of the experiment was completely

successful. Data obtained during the run should provide a value of A with

*Physikalisches Institut, Heidelberg, Germany.

tlnstitut Laue-Langevin, Grenoble, France.

46

1MVT r-T rr rI1V7 r- 1yTIII

- l~)

0000

00

to

0

Cl)

E

0U-

0

W

-o

5 10 15 20 25ELECTRON ENERGY (Channels)

--- III II III I -- --

5 10 15 20 25ELECTRON ENERGY (Channels)

Fig. 1-15. Preliminary results on the S-decay asymmetry of the neutron.The upper figure shows a typical background-subtracted electron energyspectrum. Some unsubtracted background remains at this time at lowenergies. The lower spectrum shows, as a function of electron energy,the asymmetry from polarized neutron S-decay.

2.0

O O-

0 t i i iI i i i O t m h m

1.5

1.0

0.5

0.00

0.075

0.050

0.025

0.000(/1

-0.025

-0.0500

I l l l 1 1 -#+ l 1 11 1 1 1 1 1 1 1 1 1 1 1 ll l 1 1

47

an error five times smaller than the best present values. The v/c

dependence of the asymmetry was observed for the first time and the data

are sufficient for providing a preliminary result for the energy dependence

of A. (See Fig. 1-15.) The ILL management has allocated three running

periods for this experiment during the last half of 1983. The data from

the first run are being analyzed at Heidelberg and Argonne and the

experiment is being refined and improved for the next run. Application of

the present detector to the measurement of other correlation coefficients

is under study.

h. Study of the 1 0 B(2~, 5.11 MeV) and 1 0B(2+, 5.16 MeV) Levels(S. J. Freedman and J. Napolitano)

To better evaluate the feasibility of a new effort to study

nuclear parity mixing due to the weak neutral current in 10B, we have begun

a study of the 2~-2+ doublet in 1 0 B. The resonance width of the 2 level

has been measured with the 6Li(a,y)1 0 B reaction. (See Fig. 1-16.) Values

for the total gamma decay width and the gamma decay branching ratios of

these levels were also obtained. Future experiments will be performed to

measure the a partial-wave decomposition in the 6Li(a,y)10B reaction as

well as the branching ratios for particle and gamma decays from the 2+-2-

doublet. These results will help implement a reevaluation of the current

theoretical expectation for parity mixing in 1 0 B. Possible new experiments

to measure parity mixing in 10 B are being explored.

48

>6000a)

4000

2000

1.155

500

400

300

200

100

0

L16 1.165 1.17 1.175 1.18E~ (DYNAMITRON VOLTAGE IN MV)

Fa(2)LB= (1.63 0.11) KeV

(B)

171 1 1 11 1 111III 1A~

1.065 1.07 1.075I'lILy

1.08 1.085 1.09

Ea (DYNAMITRON VOLTAGE IN MV)Fig. 1-16. (A) Thick-target resonance yield from a-capture on 6Li to the

5.16-MeV 2+, T=1 state in 10 B. The width of this state is 'i 1 eV and canbe neglected with respect to beam spread and Doppler broadening.(B) Thick-target yield from the 5.ll-MeV, 2~, T=0 state in 10B.Integrating the curve in (A) with a Lorentzian of width Fa( 2-)iAB yieldsa good fit to this data (with a total of four free parameters). Theresult Ta(2 -)LAB = 1.63 0.11 keV is consistent with an oldermeasurement reported in the literature.

(A)

1. 11 l i i II11111l

II

0

I I I I I I I I IIII

I L-Lt 1 1 1 1

1 I I 1 1 1

I I I 1 0 1I-A A a a I .

49

E. PARTICLE SEARCHES

Modern field theories are formulated in terms of particles whichhave not been experimentally observed. The experimental identificaton ofone of these particles would provide convincing evidence for the validityof the theoretical approaches. A reported observation of fractionally-charged objects in superconducting niobium led to an accelerator-basedsearch for fractionally-charged objects trapped in cryogenic materials.Grand unified field theories suggest that heavy magnetic monopoles exist.A search for slow-moving- magnetic monopoles is currently underway.

a. A Cryogenic Experiment for the Detection of Fractionally-ChargedParticles (D. Frekers, W. Henning, W. Kutschera, J. P. Schiffer,K. W. Shepard, C. Curtis* and Ch. Schmidt*)

The low-temperature physics group at Stanford has persistently

reportedly the observation of fractional charges on superconducting- Nb

balls. In these experiments a Nb ball of about 100-pg-mass is levitated in

a static magnetic field and the charge is determined from the response of

the ball to an alternating- electric field. Numerous searches in other

laboratories using-a variety of different (room-temperature) techniques

have all yielded negative or inconclusive results. We have therefore

performed an experiment with conditions similar to those of the Stanford

experiment (superconducting- Nb), however using a quite different detection

technique.

One of the intriguing features of the Stanford experiment is the

observation of frequent changes of the fractional charges when a Nb ball

touched a solid surface between successive measurements. This suggests

that the fractionally-charged particles present at liquid helium

temperature are loosely trapped in the superconducting Nb. These particles

should readily be released when the temperature is raised and collection

and acceleration in an electrostatic field should be possible. We have

therefore built a Nb-filament source which could be cooled down to 4.2*K

and rapidly heated up to several hundred *K. This source was installed on

one of the Fermilab 700-kV Cockroft-Walton injectors and energy spectra of

positively-charged particles extracted from the Nb filament were

*Fermi National Accelerator Laboratory, Batavia, Illinois.

1 G. S. LaRue, J. D. Phillips, and W. M. Fairbank, Phys. Rev. Lett. 46,

967 (1981).

50

measured. Careful scans in the interesting energy regions of 1/3 and 2/3

full energy were performed covering a mass range of about 10 MeV/c 2 to

100 GeV/c2 . No significant events were observed for a variety of different

operating conditions. In particular, no increase in counting rate was

observed when the Nb filament was heated from liquid helium to room

temperature.

The mass of the Nb filament in the present experiment was about

1000 times the mass of a Stanford Nb ball. If the fractional charges

observed at Stanford are due to particles trapped in the ball, we should

have seen 100-1000 events in the first few seconds after the heating.

Since we observed no signals above the background of 10-2 per second we

conclude that the fractional charges observed at Stanford are either

carried by particles outside the mass range of our experiment or another

hitherto unknown mechanism is responsible for their appearance.

b. A Search for Super-Heavy Particles in Cosmic Rays(S. J. Freedman, B. Gobbi,* M. Kroupa,t and J. Napolitano)

Grand unified, field theories suggest that there might exist

magnetic monopoles with masses on the order of 101 6 GeV/c2.

Astrophysicists have estimated the production of such objects in the early

universe and some such estimates predict a presently detectable

abundance. Searches for such objects have proceeded primarily along two

fronts. One makes use of flux quantization in superconductors to detect a

moving magnetic pole. The other attempts to identify particles moving with

extremely low velocities (~10~4 c) via ionization energy loss. A good

candidate for a magnetic monopole has been reported by Cabrera at Stanford

using the former technique. The difficulty with the latter technique is

that the level of ionization energy loss (with accompanied emission of

light) is uncertain.

We have undertaken a search for slow-moving particles with finite

energy loss. Using large-area plastic scintillators from a previous


tThesis Student, University of Chicago, Chicago, Illinois.

515

experiment (designed to search for the low ionization of fractionally

charged particles), we will be sensitive to particles with velocities

between 10-5 c and 10-3 c and which produce light to any appreciable

extent in plastic scintillators. The detectors we are using have been

shown to be sensitive to single photons. Therefore, we will be able to

detect monopoles (or any other slowly moving- particle) if any light is

emitted while traversing plastic scintillator.

Present efforts consist of constructing the superstructure which

holds the scintillator and approximately 1 ton of lead shielding needed to

reduce radioactive background. Data-acquisition electronics have been

designed and are being- constructed by the High Energy Physics Division.

Data-taking should be underway by winter of 1983.

c. A Search for Axions from Nuclear Decays (S. J. Freedmanand K. T. Knopfle*)

Computer studies of the sensitivity of the Max Planck Institute

(Heidelberg) crystal ball detector for observing axion decay have

continued. An attempt to obtain a 5 1 Cr source of ^5 kcuries produced for

calibration of the Homestake Solar Neutrino detector from Oak Ridge was

unsuccessful. Negotiations continue in an effort to find a suitable source

for the experiment in 1983. The experiment will search for axions decaying

into two photons after emission from nuclear decay.

*Max Planck Institute, Heidelberg, Germany.

53

F. MEASUREMENT OF THE ELECTRIC DIPOLE MOMENT OF THE NEUTRON(V. E. Krohn, G. R. Ringo, T. W. Dombeck,* M. S. Freedman,J. M. Carpenter,t and J. W. Lynn*)

The purpose of this project is to measure the electric dipole

moment (EDM) of the neutron. Such a measurement would probably constitute

the most sensitive test of time-reversal symmetry now available. The

present situation is that with about a factor of 10 improvement in

sensitivity, a whole class of gauge theories--those which explain CP

failure by introducing a new scalar field [e.g., S. Weinberg, Phys. Rev.

Lett. 37, 657 (1976)]--can be given a definitive test.

Since the measurement of the neutron EDM is fundamentally a

frequency measurement, its statistical uncertainty is inversely

proportional to the duration of the measurement. It is therefore natural

to try the measurement on ultracold neutrons (UCN). These neutrons with v

< 7 m/s can be kept in a bottle for hundreds of seconds. We propose to do

this using two unique features. First, we propose to use a pulsed neutron

source and keep the inlet to the bottle open only when the pulsed source is

on, thus allowing a buildup to an asymptotic density determined by the peak

flux of the source instead of the average. This has the advantage that

pulsed sources have peak fluxes that are much higher than the average

fluxes of steady state sources of the same average power. Second, we

propose to produce the UCN by Bragg reflection of considerably faster (400

m/s vs 7 m/s) neutrons from a moving mica crystal designed so that the

reflected neutrons are almost stationary in the laboratory system. The

advantage of this is that it avoids the problems of extracting the very

delicate UCN from the hard-to-control environment in a high flux source.

The present state of the project is that both of these ideas have

been tested and shown to be practical as have several other ideas for

enhancing the production of UCN, such as the use of reflectors around the

moving crystal and funnels to concentrate the UCN in real space at the

expense of their concentration in velocity space. The experiment has been


tlntense Pulsed Neutron Source, ANL.

*University of Maryland, College Park, Maryland.

54

seriously handicapped by the abandonment of the liquid hydrogen moderators

at IPNS and the delay in achieving 100*K moderation.

A very encouraging development however has been the news that the

macropulses of LAMPF at Los Alamos can be used on a spallation neutron

source and that they will be available at one or more places there. This

would represent a gain of a factor of at least 100 over IPNS in the

critical variable of the experiment--density of neutrons in the measurement

bottle. It should lead to a measurement of an accuracy of a few times

10-26 cm x e for the neutron EDM--approximately 10 times better than the

present limit.

55

G. GeV ELECTRON MICROTRON

There is a clearly articulated national need for a high intensityhigh-duty factor GeV electron accelerator, and the stated intention of DOE

is to consider proposals for facility construction to begin in 1985. TheGeV electron microtron (GEM) project at ANL has been engaged in an

intensive effort to develop the technology for such an initiative. GEMscientists have developed a new advanced design for an electron acceleratorwhich meets all the stated design objectives at low capital and operating

cost.1 The new accelerator, called a hexatron because of its six-sided

geometry, will furnish high-qualit" continuous beams in the energy range of800 million electron volts to 4 billion electron volts. A plan view of the

microtron laboratory is shown in Fig. 1-17. The accelerator, a variant ofthe microtron family, is compatible with an existing facility at Argonnewhich is currently unoccupied and available. The replacement cost of thatcomplex, formerly occupied by the Zero Gradient Synchrotron accelerator,would be greater than $50 million. Its use would result in major savingsin capital cost for the new national facility, a key element in the

national plan for nuclear physics. The cutaway view in Fig. 1-18 shows theaccelerator and experimental areas in the existing buildings. GEM would bethe first major high-energy electron accelerator capable of simultaneouslyserving more than one experimental area. The availability of threeindependent electron beams with variable energies in the GeV range, 100%duty factor, and currents of 100 pamps, would open a new and exciting rangeof electron nuclear research which would address many of the mostinteresting questions at the frontiers of nuclear physics. The Argonneeffort has concentrated on an engineering and design study of the sectormagnets which generate the guide fields in the multi-sided configurationswhich would be employed for GeV accelerators. A detailed conceptual designhas been completed for the sector magnets in the hexatron system. Currentefforts are focused on 3-dimensional computational simulations of the fieldprofiles, as a proof of principle demonstration of the design. Todemonstrate scientific feasibility it is necessary to determine the centraland fringe field profiles accurately and include their features in thedevelopment of a system of optical elements giving orbit containment andhigh transmission. Construction of a magnet prototype is planned. Itsdesign will closely approximate that to be used in the working hexatron,but its primary purpose is to serve as a benchmark for 3-D fieldcalculations using newly developed computational techniques. When thereliability of these calculations has been established, they will be usedto optimize the sector magnet design for the best transmitted beam qualityand minimum capital cost.

1H. E. Jackson et al., A National CW GeV Electron Microtron Laboratory,Argonne Report ANL-82-83, December 1982.

BLDG

369

.EIMRS

L T O

MEDIUM

RESOLUTIONAREA

BLDG. 370

/1/,II

BLDG. 368

DATA ROOMS

0 10 20 30 METER

0 50 100 FEE T

~I

HIGH RESOLUTION

.... 4AREA

.ti-,BLDG.

365"

H EX AT RON

MONOCHROMATIC BLDG. 371PHOTON AREA

Fig. I-17. Plan view of the ANL 4-GeV microtron facility showing three experimental areas and

associated beam transport.

U-,0N

57

J .

Fig. I-18. Pictorial view of the ZGS area. The proposed hexatron and

experimental areas are indicated in a conceptual manner. The cut-away

view of the ZGS ring building indicates the proposed location of the

hexatron. The GEM experimental areas and spectrometers are shown as

being housed in the ZGS experimental area buildings.

58

a. Workshop on High-Resolution and Large-Acceptance Spectrometers(B. Zeidman, Editor)

A workshop concerning the present status and future technological

developments for high-resolution and large-acceptance spectrometers was

held at ANL on September 8-11, 1981. The proceedings of this workshop are

available as an informal report, ANL/PHY-81-2.

b. Microtron Development

Assembly and testing of a prototype sector magnet has been

scheduled for completion in 1983. Field measurements made with a precision

of 0.1% and a spatial resolution of 0.5 mm will be completed during this

period. Subsequent calculations using 3-D magnet programs such as TOSCA

will be used to optimize the design. The results will be incorporated into

a model of beam dynamics in the hexatron for establishing accelerator

performance and the electron current threshold for beam breakup. The data

will furnish the base for evaluating alternative designs for a multi-sided

microtron. At this time a decision will be made on a final magnet

configuration which will be incorporated into a design including cost and

time schedules. A construction proposal for a multi-GeV CW electron

accelerator research facility including experimental areas has been

submitted to DOE early in 1983.

59

II. RESEARCH AT THE TANDEM AND SUPERCONDUCTING LINAC ACCELERATOR

Introduction

The completion of the superconducting linac booster has made itpossible to perform experiments on a more-or-less regular basis, withoccasional accelerator shutdown to allow for maintenance and ATLAS building-construction. The development of an improved ion source has made feasibleexperiments with "difficult" beams such as Ca and Ti. The experimentalfacilities are also nearly complete. All these factors have benefitted andstrengthened the heavy-ion research program. The overall, thrust of thisprogram continues to be the systematic study of nuclear structure at high

spin, high excitation energy, and nuclei far from stability; and thedistribution of reaction strengths with increasing- beam energy and theinfluence of nuclear structure on the reaction mechanism. Several newdirections have been developed including investigations of the relaxationprocess following fusion, momentum transfer of evaporation residues, fusionforming very heavy compound systems and shape changes in heavy transitionalnuclei.

Significant information and understanding- of shape transitions innuclei have been obtained from experiments on soft transi Sn n uclei.Striking prolate-to-oblate changes have been observed in Dy, whiledecoupled i1 3/ 1 8geutron bands with both prolate and oblate shapes have beenidentified in Hg. These studies have led to a good description of thenuclear shape as a function of spin and neutron number and to a better

appreciation of the shape-driving force provided by decoupled high-jquasiparticles. Measurements of lifetimes of continuum states and feedingtimes of high-spin yrast states indicate the coexistence of both collectiveand single-particle structures above the yrast line in transitionalnuclei. In the program on proton (h 1/2)n valence structures outside a N =82, Z = 64 core, a long-lived (40- us) isomer was discovered in $Yb82,extending the body of data which is very well predicted by shell-modelcalculations.

Cross-section measurem gts of eporation residues formed inbombardment of Sn isotopes with Ni and Ni have revealed interestingcross-section differences as a function of the neutron number of thecompound nucleus. Experiments are underway to determine whether thisneutron-number dependence is due to differences in compound nucleusformation or differences in fission competition. Residues with lowproduction cross section have been detected through delayed a activity. Theaim of these programs is to elucidate the influence of shell structure infusion, the dynamics of the fusion process, and the survival probability ofheavy residues--of relevance for the production of superheavy nuclei. Theearliest stages following fusion have been probed by measurements ofneutron spectra and neutron multiplicity distributions. Suppression ofneutron emission is observed and may be related to trapping- in asuperdeformed potential well as the initially highly deformed staterelaxes.

While it is well known that the evaporation residue cross section

ceases to increase beyond a certain center-of-mass energy, the exact causefor this phenomenon has not been unambiguously identified. The onset and

60

growth of incomplete fusion, quasifission, deep-inelastic scattering andfragmentation are responsible, but the distribution of reaction strengthwith beam energy has yet to be definitively ascertained. To determine thisdistribution systematic studies will be necessary. The experiments atArgonne focus on measurements of discrete tates2 of the velocities ofevaporation residues. In a study of the Cl + Pb reaction, which is ofthe first type, it has been observed that neutron and proton pick-upchannels dominate the transfer and deep-inelastic reactions,respectively. A broad set of singles and coincidence experiments is basedon measurements of residue velocities, which allow a decomposition of thecross sections associated with full and partial momentum transfer.Interesting- differences in the cross section for complete momentum transferhave been observed in producing the same compound nucleus with differententrance channels.

The accelerator mass spectrometry (AMS) program continues both atthe tandem and at the linac. AMS has been demonstrated to be an extreme}effective tool for measuring very low-level concentrations (10-10 to 10 )of radioisotopes. The Argonne program concentrates on nuclear-physic -related problems 6 Bnd includes the determination of the half-lives of Ti(completed) and Fe (in progress), a search for doubly-charged negatiion 1 and development of methods for detecting low concentrations (~t0 )of Ca, which may have applications for dating- in geology and archeology.

The experimental facilities associated with the linac are closeto completion. Currently being- installed are a general-purpose beam line,a beam line for the Purdue superconducting-solenoid electron spectrometer,and diagnostics and protection for the beam-line vacuum system.Improvements and upgrade of present equipment continue. A position-sensitive ionization detector has been installed in the spectrograph withgood mass, charge, energy, and position resolution, while a large-area QE-Edetector and channel-plate detectors have been built for evaporationresidue measurements. A new sophisticated plunger for recoil-distancelifetime measurements has been extensively tested and used in severalexperiments. The ANL-Iowa-Minnesota apparatus for optical-hyperfine-interaction measurements is close to completion. Finally, substantialeffort has been devoted by the research and technical staff towards plansand designs for beam-line layout, experimental equipment, and dataacquisition at ATLAS. The preparation and construction of the ATLASexperimental areas will consume an increasing- fraction of our total effortin 1983-1985.

61

A. HIGH ANGULAR MOMENTUM STATES IN NUCLEI

Our studies have concentrated on and documented several cases ofshape changes which occur at high spin. We have devoted a fair fraction ofour fort on transitional nuclei (Dy and Er isotopes with N ~ 88and Hg) since these are soft with respect to the shape degree of freedomand thus most susceptible to shape changes. We are also interested in thenaty of yrast states at very high spin and have identified statesin Gd with spins in excess of 81/2, the highest recorded spin for anyrast state. Here the level structure and feeding times suggest thepersistence of an oblate coupling scheme up to and slightly above thisspin. Efforts to investigate the structure of continuum states above the

yrast line involve measurements of lifetimes of these states, eitherdirectly or indirectly through the feeding times of yrast states. In theprogram studying the (rh 11 2)n configuration outside Z = 64 and N = 82, along-lived 10+ isomer (w{t half-life corresponding to -0.01 Weisskopfunit) was discovered in 70Yb8 2 , a nucleus very near the proton dripline. This confirms theoretical expectations for the forbidden E2 decay inthe half-filled shell (n = 6); in fact, our data on the (hll/ 2 )n couplingswith n = 3-6 show remarkably good agreement with shell-model calculations.

An active collaboration continues with Prof. P. J. Daly's groupfrom Purdue University. Several projects are also joint ventures with

overseas scientists from Copenhagen, GSI, Jyvskyld', Orsay, and Strasbourg.

a. Gamma-Spectroscopy at Very High Spins in 147 Gd (S. Bjornholm,*J. Borggreen,* J. Pedersen,* G. Sletten,* P. Chowdhury,H. Emling, D. Frekers, R. V. F. Janssens, T. L. Khoo,Y. H. Chung,t and M. Kortelahtit)

One of the striking results of the yrast population experiment

(see section A.g.) was the observation that the yrast states in 14 7Gd were

strongly populated (>80% of ground state strength) even at spin 65/2.

Gamma-gamma coincidence cx:asurements have been performed for

transitions reaching -^6 MeV above the 550-ns isomer at excitation 8.590 MeV

and spin 49/2+. In another experiment angular distributions were measured

and the analyses established spins along- the yrast line up to 79/2 and E ~

17 MeV (Fig II-1); these are the highest values of both spin and excitation

energy observed from yrast states in heavy nuclei. In all experiments an

array of 14 NaI detectors was used to select high multiplicity events which

feed the 550-ns isomer. Consequently, only Y rays feeding- the isomer were

accepted, resulting- in very clean spectra.

*Niels Bohr Institute, Denmark

tPurdue University, W. Lafayette, Indiana.

62

'47GdI Fi 9I vI,

597.4(6)

14795- ----

60

16938

1246 1086(5)

15692300.3 (6)

15177 215.5 3

741.6(8)

14435

1 9 8 6.7(10)

13418 67/2 13448

1 3106 69/2- 1 213$ 7 61208.0 6 2716.3

(3) 896.1 1414.5 ( 2550(9) (I

12210 65/2..)11853 65/2- 11932

976.4 618.6(23) 1.

W

897.9(10)

618.3

(II)

93611234 6V/2- ^ (21)10995 238.9 (42) 1 6 - O.8 nsT10749 246.2 (15) 572 54,3.6(6) 10690 304.5 (56)

10490 259.6(4) 55/21056.1 1808.9 6.3

9693124 638.8 53/2+ 9509372.7(27)49243 t(2) 51/,.12919

8590

1103.4(67)

r

653.0(2)

t

919.1(27)

*

t.,2=550ns

Fig. II-l. Level Scheme of 147Gd on top of the 49/2+ isomer located at

8.59 MeV. Spins and parities have been deduced from angular

distribution measurements.

69/2

65/2

61/2

59/p.-57/2.-

53/2.

4 9/2+t

(3

-- 1

79/ 2

75 /273/27 3/2

q

r9

b

i

i

63

Independent-particle model calculations come out with

configuration assignments in reasonable agreement with the spins and

energies measured, but they also tell us that within a few more units of

angular momentum the nucleus has to find extraordinary ways of producing

the spin, either by exciting nucleons from the next major shell or from

collective rotation.

One way to distinguish between these two modes may be a

determination of subnanosecond lifetimes and feeding times of the upper

states; for this reason Doppler shift measurements with a plunger are

planned.

b. Shape Change in 153Dy (M. Kortelahti,* Y. H. Chung,*P. J. Daly,* Z. W. Grabowski,* A. Pakkanen,* P. Chowdhury,R. V. F. Janssens, and T. L. Khoo)

The yrast configurations of nuclei with N > 90 originate from the

collective rotation of prolate shapes, while those of nuclei with N t 86

arise from the alignment of a few high-j orbitals, leading to oblate

shapes. Our studies of the transitional nucleus 15Dy8 8 have shown the

first instance of a transition from prolate to oblate shapes with

increasing spin (I > 32). 16Dy8 7 should also exhibit a similar shape

transition. Indeed Y-spectroscopic studies through the 12 4Sn (3 4 S,5n)

reaction bear out this expectation, with the oblate shapes emerging for I >41/2. The occurrence of a 2.3-ns isomer with I ~ 47/2 provides strong

evidence for this statement. The study of 1 5 3Dy completes our systematic

investigation of Dy isotopes with N = 82--88, allowing us to trace the

evolution of nuclear shapes as a function of spin and neutron number. In

the process we have observed the important role played by rotational

alignment - induced by the Coriolis force - in shape transitions.

*Purdue University, W. Lafayette, Indiana.

64

c. Lifetime Measuremencs in 15 4Dy (H. Emling,* P. Chowdhury,D. Frekers, R. V. F. Janssens, T. L. Khoo, W. KuYhn,A. Pakkanen* Y. H. Chung,* P. J. Daly,* Z. W. Grabowski,*and M. Kortelahti,*)

We have recently published in Physical Review Letters the results

of extensive Y-ray spectroscopic studies in 16Dy8 8 , which included

lifetime measurements. Levels up to spin 34 or 35 were established, and at

spin 33 a transition from collective to aligned-particle structure was

observed in a heavy nucleus for the first time. The lifetimes suggest that

this transition evolves through a series of triaxial shapes.

The earlier recoil distance lifetime measurements in 15 4Dy had

yielded results with large uncertainties for the yrast states in the spin

region between 10 and 20, owing to the strong influence of slow (10-25 ps)

side-feeding and the fact that the emphasis had been on short lifetimes

(<10 ps).

We have performed new lifetime measurements in 1 5 4 Dy, focussing

on the medium-spin states. A (34S,4n) reaction was used to populate 154Dy

at a lower excitation energy and spin, to enhance the prompt feeding into

the medium-spin range. Recoil-distance techniques were employed with a

newly constructed plunger which fits inside the sum spectrometer. The use

of the sum spectrometer made it possible to obtain very clean spectra for

the 1 54 Dy channel of interest. (A method for isolating a single reaction

channel has been found.)

The results, however, did not significantly improve the accuracy

of the extracted lifetimes, because the feeding times from the non-yrast

continuum states were slow, thereby reducing the sensitivity for measuring

short lifetimes. On the other hand, the observation of this slow component

suggests that the Y-deexcitation pathway goes through single-particle

configurations, before finally feeding into medium-spin yrast states which,

in contrast, are of collective nature. The single-particle configurations

lie above the yrast line and are probably related to the aligned-particle

structures which become yrast around spin 32. Analysis to extract the spin

dependence of the feeding times is currently underway. When completed we

should have important information for a detailed understanding of the


65

structure of the continuum states which lie above the yrast line. We plan

to identify the high-spin yrast structure of 155Ho and to measure lifetimes

here. The coupling of an additional proton to a soft 1 5 4 Dy could lead to

interesting shape changes.

d. Shape Changes at High Spin in 155Er (G. Bastin,t F. Beck,*C. Schick,t D. Frekers, R. V. F. Janssens, T. L. Khoo, W. Kuhn,and M. Kortelahti*)

The occurrence of a shape change at high spin has been

demonstrated in this laboratory for 153,1 5 4 Dy. While up to spin 41/2 and

32+, these nuclei exhibit band structures similar to those observed in the

deformed nuclei, at higher spins the level structure becomes rather

irregular and resembles the one seen in spherical or slightly oblate

nuclei. We made the suggestion that this change is due to the polarization

of the core by the alignment under rotation of nucleons located in high-j

orbitals. In order to test this hypothesis, studies of level structures in

neighboring transitional nuclei are necessary. 155Er was studied with

the 1 2 5 Te( 3 4 S,4n) reaction at 160 MeV and Y-Y coincidences, angular

distributions and an excitation function were measured. The analysis is in

progress.

*Centre de Recherches Nucleaires, Strasbourg, France.

tCentre de Spectrometrie Nucleaire et de Spectrometrie de Masse

du C.N.R.S., Orsay, France.


66

e. Lifetime Measurements of Continuum States in 154,152Er(P. Chowdhury, I. Ahmad,* R. V. F. Janssens, T. L. Khoo,W. Kuhn, G. Rosner, Y. H. Chung,t P. J. Daly,t S R. Faber,tZ. W. Grabowski,t M. Kortelahti,t J McNeill,t A. Pakkanen,tH. Emling,* and D. Ward )

Earlier measurements of the population patterns of the yrast

states in 15Dy86 , together with multiplicity and angular distribution

measurements of continuum Y rays, had yielded evidence suggesting the

presence of collective structures built on high-spin aligned-particle yrast

states in 16'Dy 86 . Direct information on the degree of collectivity can be

obtained from the lifetimes of the continuum states.

We have employed a Doppler-shift attenuation method to measure

continuum lifetimes in the Er86 and 8Er8 4 nuclei, using (6 4Ni,4n)

reactions. Continuum spectra were compared for the case where the residues

were allowed to recoil into vacuum (vrecoil ~ 0.04 c), and stopped in a Au

backing (~1.5 ps stopping times). Two 25 x 30 cm NaI crystals were gain-

stabilized and used with 10-cm diameter central Pb collimators, in

conjunction with a sum spectrometer and a Ge(Li) detector.

The use of Au stopping foils has eliminated severe normalization

problems previously encountered with Pb stopping foils, which tend to be

easily contaminated with light element impurities. The recent data are

currently being analyzed. A preliminary analysis of the 15 4Er data

suggests lifetimes consistent with a high degree of collectivity in the

continuum cascades. The lifetimes of statistical y rays with 2 MeV ( EY <

4 MeV are also of interest, in light of recent results which suggest long

decay times ('2 ps) for these y rays in 152Er. A more complete analysis is

necessary to extract the lifetimes of the statistical transitions.

*Chemistry Division, ANL.


*GSI, Darmstadt, W. Germany.

Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada.

67

f. Measurement of Feeding Times in 152Dy (H. Emling,P. Chowdhury, Y. H. Chung,* P. J. Daly,* D. Frekers,Z. W. Grabowski,* R. V. F. Janssens, T. L. Khoo,M. Kortelahti,W KuYhn, and A. Pakkanen*)

The structure of states above the yrast line can be directly

probed by a measurement of the feeding times of the yrast states. To that

effect, we have made recoil-distance measurements of feeding times for

yrast states in 1 52 Dy with a (3 4 S,4n) reaction, using a newly constructed

plunger which fits inside the sum spectrometer. This allows a study of the

feeding times as a function of sum energy, and hence as a function of

initial angular momentum. Analysis of the data is in progress.


g. Yrast Population Patterns in a Wide Range of Nuclei(J. Borggreen,* G. Sletten,* R. V. F. Janssens, P. Chowdhury,T. L. Khoo, Y. H. Chung,t P. J. Daly,t Z. Grabowski,tand M. Kortelahtit)

The purpose of this experiment is to investigate the dependence

on nuclear structure of the relative population of states on the yrast

line. We have studied the population-pattern as a function of spin in the

nuclei 148--1 56Dy, 154-- 16 0Er, 14 6,14 7Gd. The nuclei were populated

in 345- and 30 Si-induced reactions at beam energies chosen such that all

compound nuclei were obtained with similar angular momenta and excitation

energies. The analysis of the data has been completed. Striking

differences have been observed between the feeding patterns in the light

and heavy isotopes, in particular for the Dy isotopes. Indeed, -100% of

the Y-ray flux is measured along the yrast line up to the state having a

spin corresponding to the largest value that can be obtained from the

alignment of the valence nucleons on the symmetry axis (146Gd being

regarded as a core). This was observed for the nuclei 148,150,151,152Dy

which are known to have a slight oblate deformation. In contrast, in the

well-deformed prolate 154,155,156Dy nuclei, the intensity along the yrast

*Niels Bohr Institute, Copenhagen, Denmark.


68

line drops gradually starting from the lowest spin states. These findings

are correlated with the nuclear structure, the level density in the

vicinity of the yrast line and with the Y decay properties of the states

populated. Calculations are currently underway by S. Aberg (Nordita).

Preliminary results indicate that the main experimental trends can be

accounted for with level densities obtained from the deformed independent-

particle model.

h. The (ih 11 1?)6 Spectrum in 1 Yb?(Y. H. Chung,* P. J. Daly,*

Z. W. Grabowski,* M. Kortelahti,* J. McNeill,* P. Chowdhury,R. V. F. Janssens, T L. Khoo, R. D. Lawson, and H. Emling)

In continuation of our systematic study of N = 82 nuclei above

the N = 82 and Z = 64 doubly closed shells, we have investigated the

nucleus 9Yb82. Shell-model calculations, using 6 Gd8 2 as a closed core,648

have been extremely successful in describing the (h 1 1/2)6 level structure

in the 3, 4 and 5 proton nuclei 14911, 15 0Er and 1ilTm, respectively.in67 68 69 pciey

A 9 6 Ru( 5 8 Ni,2p) 1 5 2 Yb reaction was employed in conjunction with a

newly installed beam deflector system, which was used to pulce the beam. A

40's 10+ isomer was found. Both the halflife (^O.01 Weisskopf unit) of the

10+ state and the transitions below the 10+ isomer are in excellent

agreement with theory. The 10+ + 8+ decay is forbidden in the half-filled

hll / 2 proton shell and hence is expected to have a long lifetime for E2

decay. An alternative decay of the 10+ involves a 10+ + 7~ E3

transition. The experimentally observed decay of the 10+ is seen to

proceed strongly through the 7~, 5~, and 3 states to the 0+ state, as

expected from the theoretical calculations.


69

i. Spectroscopy of 10 0Cd (L. Clemann,* M. Barclay,*D. Cacic,* W. C. Ma,* C. Maguire,* J. Hamilton,* D. Frekers,R. V. F. Janssens, and T. L. Khoo,

By taking advantage of the fact that heavy-ion reactions can be

used to produce nuclei far from stability, the reaction 4 6 Ti( 5 8 Ni,2p2n) has

been used to study the spectrum of the very neutron-deficient nucleus

10 0Cd. 1000d in its ground state has a g7/2 neutron pair and a proton hole

outside the N = 50 closed shell and it is expected that these

configurations will have a considerable influence on the yrast spectrum.

The spectroscopy of Cd isotopes with larger neutron number is reasonably

well known, and information on 100Cd will make it possible to trace the

evolution o' different shapes as the neutron number increases from the

closed shell N = 50. In the experiment we used the technique of Y - Y

coincidences in conjunction with the sum spectrometer to identify

transitions in 1 0 Cd. The analysis of the data is in progress.

*Vanderbilt University, Nashville, Tennessee.

j. Prolate and Oblate Rotational Bands in 186Hg(R. V. F. Janssens, D. Frekers, P. Chowdhury, H. Emling,T. L. Khoo, W. Ku'hn, Y. H. Chung,* P. J. Daly,* Z. Grabowski,*

and M. Kortelahti*)

The light Hg isotopes are located in a transitional region

between spherical or slightly oblate nuclei and the well-deformed prolate

rare earth nuclei. Evidence for shape coexistence has been reported for

the light even-even Hg isotopes (i.e., A = 188--184). These nuclei have a

small oblate ground-state deformation as well as a prolate minimum located

slightly higher in energy ('500 keV). The present study aims at

investigating the properties of the bands located in both minima. 18 6Hg

was extensively studied this year with the 1 56Gd (3 4S,4n) reaction at 165

MeV though Y-Y coincidence, angular distribution and excitation function

measurements. A level scheme (Fig. 11-2) has been deduced which shows the

following main features: (i) the ground band is seen up to 6+ and probably

8+, (ii) the rotational band built on the prolate deformation is


70

2

5115.8 20

[5.9] 666.8

4448,9, 8f

[9.6]I 636.6

3812.3 16+

[10.1]I 611.0

[25.0]I

2619.7

2251.7

[2.7] 575.1

1

[33.9]

[57.5]

3

5347.5 (22+)

[6.2] 572.3

4775.2 20+

[I1.0] 506.9

4268.3,

[13.7]3827.3

[~ 15]3470.6,

[16.6]

3088.8[i !.I]

581.6 2833.3

12+

542.0

10+

488.9 '(0)

1588.8, 8

596.1 [73.3] 424.2

(4+) 1164.6,6+

~81] 356.7

675.2 879 4

p 620.7 2+

,2+ 522 0+

405.3 Hg86H080 106

I8*

441.0I6+

356.7_14+

381.8

12+255.5

10

(

Fig. 11-2. Level scheme of 186Hg.

[~5].1080.5,,

405.3

[100]0

I

[8.5]|

identified up to 20+ and shows a gentle upbending between levels with spin

14+ and 18+, (iii) a new band is seen from 10+ to 22+. It crosses the

band discussed in (ii) at I7 = 16+ without any apparent interaction. This

band feeds the prolate band at 10+ and shows also an irregularity in the

energy spacings between the 12+ and 14+ levels.

Calculations in the framework of the Cranked Shell Model have

been performed by S. Frauendorf and Z. Y. Zhang (University of

Tennessee). The upbend described in (ii) is explained by the crossing of

the prolate groundband by an aligned 11 3 /2 neutron band. The interaction

between the bands is strong and, hence, only an upbending is predicted, in

agreement with the data. The computed critical frequency and the gain in

alignment resulting from the interaction are in good agreement with the

experiment. The same calculations also account for the behavior of the new

band. Here again i1 3 / 2 neutrons are playing a major role but the motion

takes place in the oblate minimum. In particular, the absence of

interaction and the difference between the energy spacings in the two bands

are well accounted for. These data represent the first case where the

decoupling of 11 3 /2 neutrons is observed simultaneously for two different

deformations. Further confirmation of this interpretation will be provided

by an investigation of the odd-even isotopes 185,18 7 Hg which is planned for

next year. A 80-us isomer was also observed in 1 8 6 Hg. The analysis of its

decay is currently underway.

73

B. FUSION OF HEAVY IONS

The availability of high-quality beams with masses A >,60 andwith energies sufficient to overcome the Coulomb barrier for even theheaviest targets, has resulted in increased study of the fusion process insuck heavy systems. These efforts represent a natural extension ofprevious work with lighter projectiles that has been done in past yearswith the tandem accelerator. Of particular interest is whether nuclearstructure effects are observed in the fusion of two such heavy ions, aswell as the detailed nature of the fusion dynamics near and above thefusion barrier. A recently developed electrostatic-deflector system hasbeen used to separate evaporation residues near 0* from the beamparticles. Nuclei far from the line of stability have been produced andtheir delayed a activity has been studied after implantation in a surface-barrier detector. In addition, the average atomic charge states ofevaporation residues have been measured using this deflector system. Whencoupled with the delayed-alpha-activity measurements we can now study theprobability for compound nuclear survival with cross sections in the micro-barn region.

To gain information on the relaxation dynamics following theinitial contact of two fusing ions (for which there exists little data) wehave measured neutron spectra and neutron multiplicity distributions incold fusion reactions. Comparison with statistical-model calculationssuggest that there is a suppression of neutron emission. This may possiblybe related to trapping in a superdeformed well as the highly deformedinitial state relaxes to the equilibrium shape.

a. Fusion of 64Ni + 1 1 2 ,1 14 ,116,118,1 2 0 ,1 2 2 ,1 2 4Sn (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, W. KuYhn, F. W. Prosser,*J. P. Schiffer, and B. Zeidman)

Detailed measurements of evaporation residue yields following

fusion reactions for the 64Ni + Sn system have been obtained. Excitation

functions for 6 4Ni ions incident on the even-mass Sn isotopes were measured

over the energy range 235 < Elab < 310 MeV. (See Fig. 11-3.) An

electrostatic deflector placed after the target was used to separate the

evaporation residues emerging from the target near Blab = 00 from the

intense flux of beam particles. An improved detector allowed measurements

of angular distributions at up to four angles in a plane perpendicular to

the deflection plane. When combined with our previous measurements using5 8Ni projectiles on the same Sn isotopes, the compound nuclei produced

varied in neutron number by 18 neutrons, a change of 20%. We find that the

maximum yields for all compound nuclei occur near 170--180 MeV (c.m.) with

*University of Kansas, Lawrence, Kansas.

00

I0

0.I

- I III I 1 1

5Ni + Sn

-5 A-S

-Ow

~ Iv

~ j

-1

150 160 170 180 190 200 210 150E(MeV)

c.m.

- I I I I I I I -

- 84 AN Ni+ Sn

--- O-0--

-o

I o " 124o122.1204/C o118 A318 Sn _

"116

" I 112

I I I I I

160 170 180 190 200 210

even-mass Sn isotopesFig. 11-3. Evaporation residue cross sections for 58,64Ni fusing with the(A = 112-124). Lines are drawn only to guide the eye.

E

bv

'

I, , t1 i .

T

75

the maximum cross sections increasing by about one order of magnitude

from 58Ni + 114Sn to 64Ni + 124Sn. (See Fig. 11-4.) These results allow a

systematic study of compound nucleus survivability in systems for which

fission competition becomes increasingly important. Related topics of

current interest include possible entrance channel effects and whether an

"extra-push" energy is needed to achieve fusion in such heavy systems. To

further understand the fusion process, we plan to extend our study of the

64Ni + Sn system by measuring fission excitation functions over the same

energy range.

b. Fusion of 58Ni + 112,114,116,118,120,122, 1 2 4Sn (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, T. J. Humanic, W. Kuhn,F. W. Prosser,* J. P. Schiffer, and B. Zeidman)

We have measured, at selected energies, the angular distributions

of the evaporation residue yield from the fusion of 58Ni with the even-mass

Sn isotopes using our improved AE-E detector assembly and electrostatic

deflector. These measurements allowed us to fix the absolute

normalizations of our more extensive Blab = 00 excitation function which we

had obtained with our earlier, single AE-E counter. As a result, we were

able to compare excitation functions leading to the same compound nucleus

for 5 8Ni + 12 4Sn and 64Ni + 118Sn. The excitation functions for the two

entrance channels have similar shapes with the 6 4Ni + "18Sn data having

slightly large cross sections above the barrier. The implications

regarding the statistical model and possible entrance-channels effects are

currently being assessed.


c. Fission of 64Ni + 112,114,116,118,120,122,124Sn(W. S. Freeman, D. F. Geesaman, W. KuYhn, G. Rosner,J. P. Schiffer, and B. Zeidman)

We have recently begun a series of measurements of the fission

yields from 64Ni + Sn. These results, when combined with our evaporation

residue (ER) cross section measurements for the same systems, will give

information on the complete fusion (fission + ER) cross sections near and

above the classical fusion barrier. Of particular interest is whether the

76

' I ' I ' 1 ' 1 ' I inuh1EI

64o Ni + Sn

200 - 58" Ni+Sn

180MeV (c.m.)

I50-

Eo:

bw100

50

170 174 178 182 186 190Ac4 CN.

rig. 11-4. Values of aER as a function of the compound nucleus mass for5 8,6 4Ni+Sn at E = 180 MeV. The open (filled) circles denote6 4Ni(5 8Ni) as t m projectile. The solid (broken)-line histo rramsare the results of statistical-model calculations with 6 4Ni( 8Ni) asthe projectile.

77

observed target (or compound nucleus) mass dependence of the ER cross

sections above the barrier reflect differences in the fusion cross sections

or differences in the fission competition. To date, one experiment has

been performed at incident energies of Elab = 275 and 320 MeV for which the

data analysis is in progress.

d. Delayed Alpha-Decay of Evaporation Residues Formedin Fusion Reactions (W. S. Freeman, D. F. Geesaman,W. Henning, W. Kuhn, G. Rosner and B. Zeidman)

Delayed alpha decays of the evaporation residues formed following

the complete fusion of two heavy ions were observed after their

implantation in silicon surface-barrier detectors placed near 0lab = 00.

The electrostatic-deflector system used in our fusion cross-section

measurements was utilized to separate the evaporation residues from the

beam. Measurement of the delayed alpha energies and lifetimes provides a

powerful additional means of particle identification and allows the

measurement of lower evaporation residue cross sections. To ascertain the

sensitivity of this technique with our present experimental configuration,

we searched for delayed activity using 5 8Ni and 3 7C1 beams bombarding

several targets spanning a broad mass range. The heaviest target-

projectile combination for which we observed delayed alpha activity

was 37C1 + 17 1Yb which forms the compound nucleus 208Fr. These results

showed background contributions in the ac-particle spectrum at a cross-

section level of ~2 b, two orders of magnitude better than our sensitivity

using the standard AE-E method. Additionally, c-decay measurements have

been made following the fusion of 5 8Ni + 1 1 2 ,114Sn which form the proton-

rich compound nuclei 1 70 ,17 2 Pt. These nuclei are in a region where there

is little information with regard to masses or lifetimes. The data are

presently being analyzed.

78

1.0

1.5

6 8

/ELABq

2.0

10

(M:V)

12

2.5

14

3.0

16

FIELD STRENGTH (kV/cm)

Fig. 11-5. The relative evaporation residue yield for 58Ni + 4,124Sn

as a function of the deflector electric field strength (lower scale) and

the average energy-to-charge state ratio (upper scale for EM = 281 MeV.

0

1-

wi

I I

I

+opsf

j/ "58N +124S

10 58Ni+ 1 Sn

I1 i

I I I I

0.5

1

I | I I

79

e. Atomic Charge States of Evaporation Residues (W. S. Freeman,D. F. Geesaman, W. Henning, W. Ku'hn, F. W. Prosser,*J. P. Schiffer, and B. Zeidman)

In the course of our measurements of evaporation residues formed

in heavy-ion fusion reactions (e.g. Ni + Sn), we have employed an

electrostatic deflector after the target to separate the low-energy,

highly-charged fusion products from the beam. The deflector separates

particles according to their charge-to-energy ratio. A knowledge of the

average energy of the evaporation residues, which is set by the kinematics

of the fusion reaction, together with the known experimental geometry then

enables a determination of the average atomic charge state. (See

Fig. 11-5.) We find charge states for Ni + Sn fusion products that are 6--

13 units higher than the equilibrium value expected for stripping in the

target (at E{a(Ni) - 280 MeV). This suggests that nuclear decays after

the target foil (e.g. internal conversion and Auger electrons) play an

important role. As has been previously realized, these anomalously high

charge states have potential implications for fusion measurements that

employ recoil mass spectrometers or velocity filters with additional

focussing elements that are sensitive to the atomic charge state.

We plan to extend our fusion cross-section measurements, using

the deflector, to heavier systems. As a byproduct, these measurements will

also provide additional information on the average atomic charge states of

these heavier evaporation residues.


f. Prompt Compound-Nuclear K X-rays in Fusion Reactions Inducedby a Heavy Projectile (H. Ernst, W. Henning, C. N. Davids,W. S. Freeman, T. J. Humanic, M. Paul,* and S. J. Sanderst)

The limits of complete fusion and compound-nucleus formation in a

nuclear reaction induced by a heavy projectile are currently of great

interest. We have studied prompt K X-rays in compound-nuclear reactions

induced by a heavy projectile, by determining total production cross

*Hebrew University, Jerusalem, Israel.

tYale University, New Haven, Connecticut.

80

sections and multiplicities of K X-rays for the systems 32 + 116,120,124Sn

from X-ray singles, X-ray--X-ray coincidences, and direct evaporation

residue yields over the incident energy range 130 MeV < Elab < 202 MeV. We

find a slow dependence of the multiplicities and cross sections on target

mass and incident energy, establishing the prompt K X-ray yields as a

reliable indicator of the complete fusion cross section behavior induced by

a heavy projectile in this mass region. This work has been recently

completed and published in Physics Letters.

g. Suppression of Neutron Emission in 'Cold' Heavy-Ion Fusion(W. Kuhn, P. Chowdhury, R. V. F. Janssens, T. L. Khoo,F. Haas,* J. Kasagi,* and R. M. Ronningen*)

In "cold" heavy-ion fusion reactions, where the excitation energy

is low (E* < 50 MeV), the relaxation of the initially highly-deformed

nucleus may be influenced by shell effects. For example, the system may be

trapped in a secondary minimum in the potential energy surface

corresponding to a larger deformation than normally observed near the

ground state. We have studied the system 64Ni + 92Zr, forming the compound

system 156Er with E* = 46 MeV. Measurements have been made of the relative

yields of the neutron-emission channels (Fig. 11-6) and of the neutron

spectra corresponding to different Y-sum energies (Fig. 11-7). When

compared with the results of statistical model calculations, with

parameters constrained to fit all available data, the experimental 2n/3n

ratio is ~ 38 times larger. Thus there seems to be a suppression of

neutron emission. One possible reason for this is that there is trapping

in a potential well, as described above, for a time longer than that for

neutron emission. The available energy for neutron emission is then

reduced, leading to the emission of fewer neutrons than might otherwise

have been expected.

If this speculation is correct, there are several consequences

which can be experimentally observed, e.g. in the energy distribution of

the continuum Y-ray spectrum. Future experiments will be directed towards

the search for the evidence necessary to confirm the suggestion of

deformation traps.

*Michigan State University, East Lansing, Michigan.

81

* 50

L

> 10-j 5

I 2 3 4NEUTRON MULTIPLICITY

Fig. 11-6. Comparison of experimental (open circles) neutron

multiplicity distribution with those from statistical-modelcalculations using the normal (solid bars) and elevated (dashed bars)

yrast lines.

82

6I0

-C

"

0

4I0

Siv

510

zOIo

-I

0

w)

L>u

He

2.5

2.0

1.5)

2

10

4 6C.M.- ENERGY (MeV)

20SPIN

30

8

40(i)

Fig. II-7. (a) Neutron spectra, measured at 00, for six different gamma-raysum energy slices. The straight lines represent fits with an exponential

function. Deviations from the exponential shape at high sum energy aredue to contamination from isomeric gamma rays. (b) Temperatures, derivedfrom the fits in (a), as a function of mean entry line spin corresponding

to the different sum slices. The solid line represents results fromCASCADE calculations, using an yrast line elevated %10 MeV with respectto the known one.

HIGH SUM ENERGY (a)

TLOW SUM ENERGY

10

- -I

. (b .

AOM4,

83

C. REACTION MECHANISMS AND DISTRIBUTION OF REACTION STRENGTHS

Studies of reaction mechanisms and distribution of reactionstrengths have continued to be extended to higher energies, heavierprojectiles, and heavier target nuclei as the accelerator capability hasincreased. Transitions to distinct final states produced in reactionsinduces 7by both lighter projectiles (e.g. 0) and heavier projectiles(e.g. Cl) have been studied to better understand the energy andprojectile dependence of direct processes and the transition fromquasielastic to strongly-damped processes. Velocity spectra ofindividually-resolved evaporation residue-like masses have been used inboth singles and coincidence measurements to obtain evidence of significantcross sections for incomplete fusion processes at higher bombardingenergies for some projectile-target systems.

a. Rgacti s to Resolved States and Nonfusion Channels for0 + Ca at Elab = 158.2 MeV (T. J. Humanic, H. Ernst,

W. Henning, and B. Zeidman)

Elastic scattering, inelastic scattering and single-nucleon

transfer cross sections to resolved states were measured for the 160 + 4 8Ca

system at Elab = 158.2 MeV. In addition the total nonfusion reaction cross

section was determined. This study is part of an investigation of energy

dependence of the reaction cross sections in the 160 + 48Ca systems and a

test of the DWBA model as well as other reaction models. Qualitative

agreement between the experimental results and DWBA predictions was found

for a number of resolved states. The results have been published in

Physical Review.

b. Elastic Sca ering4 nd Single-N leon Transfer ReactionsInduced by 60 on Ca at lab( 0) = 150 MeV (G. Stephans,D. G. Kovar, H. Ikezoe, J. Kol a;,R.-Pardo, K. E. Rehm,G. Rosner, and R. Vojtech*)

Angular distributions for elastic and inelastic scattering, and

for the single-nucleon transfer reactions (160,150), (160,1 5N), (160,170),

and (160,1 7F) to low-lying states of the projectile- and target-like

ejectiles have been measured at Elab(1 60) = 150 MeV using the split-pole

magnetic spectrograph. Using beams from the tandem--linac accelerator,

energy resolutions of "175 keV were obtained. Similar data have been

*University of Notre Dame, Notre Dame, Indiana.

84

I I I I I I I I I I I * I I I I I I I I 140 640 16

Ca + 0

TRANSFER REACTIONS

17 39c Og.s.+ Ca g.s.17 39 -

o 17Fg.s.+ K g.s. _

15 41o Ng.s.+ Scg.s. -

15 41-x Og.s.+ Cag.s.

--.------ Avg.= 0.99 -

O-

000

X

_ X

a . I I * a a a I I II I a I a I50 75 100 125

EIb( 0)

1

150 175

Fig. 11-8. Ratio of integrated DWBA cross sections to experimental crosssections for all single-nucleon transfers to projectile-target ground

states are plotted versus 160 bombarding energy. Results for 56 and75 MeV are from Ref. 1 and for 150 MeV are from the present study.

2.0-

I.5-

0 I.OH

O.5

'

I I l l 1 l l l l

I

85

obtained at lower energies1 and the present data play an important role in

establishing the cross-section behavior as a function of bombarding

energy. For the elastic and inelastic scattering of interest is the

apparent increasing importance of the inelastic excitation of the

projectile and questions regarding the importance of coupled-channel

effects. For the transfer reactions the interest is in how well DWBA

(CCBA) calculations reproduce the energy dependence of the cross sections

at bombarding energies significantly above the Coulomb barrier. The data

have been analyzed and compared with preliminary DWBA calculations. How

well DWBA predicts the cross section behavior is shown in Fig. 11-8 when

the ratios of integrated DWBA cross sections to experimental cross sections

for all single-nucleon transfers linking to projectile-target ground states

are plotted. The trend toward overprediction by the DWBA, which was

indicated by the lower energy data, is not seen in our preliminary analysis

of the higher-energy data of the present study. This result differs from

that found for 160 or 208Pb, when a roughly monotonic trend of

underprediction at low bombarding energies and overprediction at higher

energies was reported.2 However, the present, work is similar to the

analysis of 160 on 4 8 Ca, where the a(DWBA)/a(exp) ratio was found to be

essentially identical at 56 and 158.2 MeV beam energies.3 Future studies

of the increasing importance of inelastic scattering and transfer reactions

to unbound states of the projectile-like ejectiles and the projectile

dependence of direct reaction processes involving heavier projectiles are

being planned.

'E. Rehm et al., Phys. Rev. C 25, 1915 (1982); D. Kovar et al., Bull.

Am. Phys. Soc. 22, 564 (1978); C. Olmer et al., Bull. Am. Phys. Soc. 23,

941 (1978).

2S. C. Pieper et al., Phys. Rev. C 18, 180 (1978); C. Olmer et al.,

Phys. Rev. C 18, 205 (1978).

3T. J. Humanic et al., Phys. Rev. C 26, 993 (1982).

86

c. Measurements of Evaporation Residues Produced in 160 + 2 4Mg at4 -Elan( 0) < 9.5 MeV/A (D. G. Kovar, R. R. Betts,*P. Chowdhury, D. Henderson,* T. J. Humanic, H. Ikezoe,R. V. F. Janssens, W. Kuhn, G. Rosner, B. Wilkins,*and K. L. Wolf*)

Time-of-flight singles measurements resolving the individual

masses of the evaporation residues were performed at Elab(160) = 59.5 MeV

to complete measurements begun last year.I Results of these measurements

showed that the centroids of the velocity spectra of evaporation residues

at 59.5 MeV are consistent with that expected for complete fusion, whereas

those at 100 MeV and 150 MeV showed deviations of ^2% and 5%,

respectively. Comparisons of the predictions of the evaporation code

LOLITA with the experimental results indicate that at Elab(160) = 59.5

MeV. The velocity spectra, angular distributions, and to a somewhat lesser

degree the mass distribution are well reproduced. At Elab = 150 MeV the

centroids of the velocity spectra ,f evaporation residues are poorly

reproduced and if one performs a detailed comparison as function of angle

only ^-600 mb of the X950 mb of evaporation residue-like cross section is

consistent with complete fusion. A coincidence measurement of individual

mass residues with protons and alphas was performed at Elab(1 60) = 150 MeV

in an attempt to distinguish more quantitatively the contributions of

incomplete fusion processes by observations of energetic protons and alphas

which are inconsistent with statistical evaporation. The results of

measurements at four angles (230, -8*, -18 , and -28*) for light-particles

and one angle (0 lab = 80) for the residue have been analyzed. Shown in

Fig. 11-9 are the alpha-particle velocity spectra (9L = -18*) observed in

coincidence with the various final particle masses detected at = 80.

Evidence for high energy (e.g., beam velocity) protons and alphas is

clearly observed in the measurements and comparisons with model predictions

for complete fusion are being made at the present time. Pending the

results of the analysis, a program of measurements to distinguish

incomplete and complete fusion processes via coincidence measurements may

be indicated. Such information would be of interest since at the present

time quantitative cross sections for incomplete and complete fusion cross

sections at higher energies are almost nonexistent.


1T. Humanic et al., Bull. Am. Phys. Soc. 27, 478 (1982).

87

" """ N M " .o sol """"S."+ .. "N " " ""so" " " " "g. r" " 4 " " ".

" N .u* w " *i " ..w M NU " "

" "g" I is " rn. " M " N ". N.

.S ..mr 494 nm.of owa s 40* .N Nto. " "

." "" ..."+ oM"+" o" " ""

" o " "" 0401 «m "yM, 04, "", N m " "*

""" eve0n. ~ memm .

.j4 IeemmA "e5"N" " " one M

-"""N * 1 w"p "" M """" .

160 +24M

E =150MeVlab&HI 8

& (~80

3 5Va (cm/ns)

7 9

Fig. 11-9. Velocity spectrum of alpha particles (0 - -18*) detected

in coincidence with the various mass heavy-ion products observed at

0HI - 8*.

38

34-

30

26

22

18

14

l0l-

U)

U)

w0nU)LU:

6

21 1

'II

'II

'I |

I I I II I I.I

I

88

d. Tim of-Flight Measurements of Evaporation Residues Producedin Si-Induced Reactions (G. Rosner, D. G. Kovar,P. Chowdhurv D. Henderson,* H. Ikezoe, R. Janssens, W. KuYhn,G. Stephans, B. Wilkins,* J. Hinnefeld,t J. Kolata,tand F. Prosser, Jr.*)

Angular distributions of velocity cross sections 1/v2 d2 a/d \dR of

fusion evaporation residues (ER) were measured for 1 60(ELab = 150 MeV)

and 2 8Si (Eab = 175, 214, 219, and 263 MeV) induced reactions on targets

of 12C, 24Mg, 2 7A1 28Si and 40Ca. The reaction products were identified

by mass (cm ~ Et2) using 2 channel-plate detectors (start,stop) and a

surface barrier detector (stop,E). A typical velocity versus mass spectrum

is shown in Fig. II-10.

Previous studies suggest that for asymmetric systems (light

projectile, heavier target) incomplete fusion or incomplete momentum

transfer occurs at Elab/A >, 5 MeV. The average ER velocities have been

reported to be appreciably smaller than the velocity of the center-of-

mass. The intention of the present set of experiments was to study in more

detail the projectile-target dependence of this behavior and to single out

entrance channel effects by forming the same compound nucleus 56Ni via 160

+ 40Ca and 28Si + 28Si. It is found that the tota,ER cross sections

for 28Si + 2 8Si are significantly smaller than those for 160 + 40Ca at

comparable center-of-mass energies. While the velocity spectra observed

for 2 8Si + 28Si are in good agreement with the predictions of complete

fusion calculations (LILITA), those for 160 + 40Ca show significant

discrepancies. Both observations indicate that ER formation in 2 8Si + 28i

is essentially due to complete fusion at the bombarding energies measured,

while the excess of ER cross sections in 160 + 'Ca stems from incomplete

fusion processes. A comparison with ER velocity cross sections for the

other fusion reactions measured is underway.


tUniversity of Notre Dame, Notre Dame, Indiana.


89

-- ATT!II! 2 8 Si +

40

36 40"32

27AlI

8 b

la

E = 219 MeVla b

J

V

28

. I I I

2800I I . I

3600I I I I

Et (arbitrary units)

I I I

4400I

5200

Fig. II-10. Velocity versus mass spectrum of the reaction 219 MeV28Si + 27A1 - ER + x, measured at Elab = 5*. The fusion evaporationresidues (ER) are centered around mass 44 amu.

i"

.:-

--"

3.6

3.2

2.8

2.41-

2.0

1 .61-

(0

EV

-

-JLi

0.8

O.4- MASS(amu)

vJ

2000

Tom'1

44

1

90

e. Fusion Cross Section Measuren.ents for 2 0 Ne + 4 Ca at

E lah(2Ne) = 150 and 220 MeV (D. G. Kovar, W. Bohne,*M. Burgel,* Ch. Egelhaaf,* H. Fuchs,* A. Gamp,* K. Grabisch,*H. Homeyer,* H. Morgenstern,* and W. Rauch*)

At the present time large uncertainties exist regarding the

experimental cross sections for complete fusion at energies Elab > 7 MeV/A

because of the presence of incomplete fusion processes. Time-of-flight

(TOF) measurements resolving the individual masses allow inspection of the

velocity spectra of the eva oration residue-like fragments. For the 20Ne

+ 4 0Ca system at Elab(2 0Ne) = 291 MeV the velocity spectra revealed

centroids significantly smaller (~10%) than that expected for complete

fusion (i.e., complete momentum transfer), suggesting the presence of

contributions from incomplete fusion and providing an indication of their

magnitude.1 In the present study TOF measurements were performed for

the 2 0 Ne + 4 0Ca reaction at Ela5 ( 2 0 Ne) = 150 and 220 MeV to establish the

systematics of the departure of the centroids of the evaporation residue

velocity spectra from that of full momentum transfer a as function of

bombarding energy and to attempt to establish the cross sections for

complete and incomplete fusion. The experiments were performed at the

VICKSI facility at the Hahn Meitner Institut, Berlin, where the

measurements provided unambiguous mass resolutions for the heaviest

residues detected (m < 54 amu). The analysis of the data is underway at

this time. Plans for the future involve extension of these measurements to

higher energies (15 < Elab ' 35 MeV/A) to explore the use of velocity

spectra as an observable for distinguishing complete and incomplete fusion

processes.

*Hahn Meitner Institut, Berlin, Germany.

1H. Morgenstern et al., Phys. Lett. 113B, 463 (1982).

91

f. Study of Direct Reactions in the System 37C1 + 208Pbat Elab = 250 MeV (K. E. Rehm, W. Kutschera, and M. Paul*)

In order to investigate the transition from quasielastic to deep

inelastic reactions we are studying the interaction between different

projectiles and 208Pb at energies not too high above the Coulomb barrier.

In a first experiment we investigated the system 37 C1 + 2 08Pb. With an

energy resolution of ^450 keV it was possible to measure the angular

distributions of elastic scattering and for the excitation of the first

excited states in 3 7Cl(l/2+) and 20 8Pb(3~). The results are shown in

Fig. 1I-11. The solid lines represent optical-model (elastic) and DWBA

(inelastic) calculations performed with the code PTOLEMY.1 From the least-

squares fit to the angular distribution for elastic scattering the

following optical potential parameters are obtained: -V = 13.1 MeV, r0 =

1.3 fm, a = 0.645 fm, -W = 5.5 MeV, r0' = 1.446 fi, a' = 0.223 fm. For the

DWBA calculations no parameters have been adjusted. The B(EL) values were

taken from the literature and the same mass and charge deformation lengths

have been used. The transfer reactions are strongly dominated by the

neutron pickup channels (37Cl,3 8C1) and (3 7C1,3 9C1), whereas deep inelastic

scattering reactions are observed mainly in the proton transfer channels

(37C1,S), (3 7 C1,P) and (3 7 C1,Al).

*Hebrew University, Jerusalem, Israel.

1M. H. Macfarlane and S. C. Pieper, ANL Report ANL-76-l1, Rev. 1.

g. Spectroscopic Studies of 2 3 4Th with the (180,160) Reaction(K. E. Rehm, D. Frekers, T. Humanic, R. V. F. Janssens,T. L. Khoo, and W. Kutschera)

The ground-state rotational band of 2 34Th has been investigated

with particle-Y techniques using the split pole magnetic spectrograph.

Outgoing particles from the reaction 180 + 2 32Th at Elab - 130 MeV were

momentum analyzed in the spectrograph at a solid angle of 5.6 mar and

detected by the position-sensitive AE-E ionization chamber in the focal

plane. Ray-tracing techniques were used to correct the AE and Be

signals. Gamma rays coincident to different particle groups in the

outgoing channel were detected in an 80-cm3 or cc GeLi detector, positioned

92

I I I I I

371C+ oePb

- EOb=250MeV

ELASTIC

- Cl (1/2+)E =I.727 MeV1

2)0 8 Pb (Y)

Ex= 2.615MeV

I I I I I I

300 40 50* 600 700 800

Bc.m.

Fig. II--11. Angular distributions for elastic scattering and inelasticexcitation of the 1/2+ state in 3 7 C1 and the 3~ state in 208Pb,respectively, as measured in the system 3 7C1 + 20 8Pb at Elab = 250 MeV.

b

b

0.I

'!)

E

C;

b-O10

'

I

I

93

827.4

556.9

333.1

162.12

49.37-0

2 3 2 Th

10+ (851.7)

8+ 567.6

6+ 338.3

4+.

20+

Fig. 11-12. Energy levels for 232Th and 234Th.

163.9

49.40

2 3 4 T h

94

10 cm from the target. Previously only the 2+ state in 2 34Th has been

unambiguously identified. In our experiment states up to I = 8(10) could

be observed (see Fig. 11-12). An attempt to increase the momentum transfer

using the (170,150) reaction was not successful. In future experiments we

plan to replace the GeLi detector with an electron spectrometer for higher

detection efficiency.

h. Large Neutron-Transfi Cross Sections Observed in 5 8Ni and 4 8TiInduced Reaction on Pb (K. E. Rehm, D. Kovar, W. Kutschera,G. Stephans, and J. Yntema)

Reactions induced by medium-weight and very heavy projectiles are

usually thought to be dominated by deep inelastic reactions. Quasielastic

reactions are expected to contribute only a small fraction to the total

reaction cross section. We have investigated mass and charge transfer

reactions induced by 4 8Ti and 58Ni projectiles on 2 0 8Pb at energies about

25% above the Coulomb barrier. The particles in the outgoing channel were

momentum analyzed in the split-pole magnetic spectrograph and detected in

the focal plane by a position-sensitive AE-E ionization chamber. The

particle identification allowed the separation of individual elements and

isotopes around 4 8Ti and 58Ni. Figure 11-13 shows a mass spectrum for Z =

28 particles with a mass resolution Am/m < 6 x 10-3. The energy resolution

was limited by the 2 08Pb target thickness (100 pg/cm2) to about 800 keV.

Both 5 8Ni and 4 8Ti induced reactions show a deep inelastic reaction

component, which is well pronounded especially at forward angles.

Quasielastic reactions, however, are not negligible. Figure 11-14 shows

angular distributions for elastic and inelastic scattering and for the

(5 8Ni,5 9Ni) and (58Ni,6 0Ni) reactions, integrated over all excitation

energies. The total cross section for 1- and 2-neutron pickup is 260 mb

and 62 mb, respectively smounting to about 25% of the total reaction cross

section, as estimated from the quarter point angle. Differences in the

mass and charge flow observed for 4 8 Ti and 5 8 Ni induced reactions can be

explained by the underlying driving potentials.

95

I I

208'' I I I I I I

5 8

eN

650CHANNEL

i+ CvPb

b=375 MeV

b= 6 5 *

28

M=59

M=60

M=s

700NUMBER

Fig. 11-13. Mass spectrum for Z = 28.observed for 375-MeV 58Ni + 208Pb

at 6lab = 65*.

2001-

57

Eu mU.

150-

1001-

-JLuzzI

I-z00a

50

0r. fa - - m

I600

- -

M=6

I

I

F .

96

'01

b:

b

0.1

100

10

58Ni ,59Ni)

5864(58Ni, 0Ni)

1000 1200

Fig. II- . Ag ular distributions forand ( Ni, Ni) reactions on 208Pb

elastic

at Elab

+ inelastic (58Ni, 59Ni)= 375 MeV.

58Ni +208Pb

Elb =375MeV

ELASTIC +INELASTIC

E

b-o

00

o 200 40 80'600

ec.m.

--- ---T---

_ _ i _ _ i _

ldk A AdIL

i i i i I

tI

97/9

i. Observation of Characteristic Ga a RaygsfromlQuasi-Elastic andDeep-Inelastic Fragments in the Ni + Ni Reaction (W. Kuhn,P. Chowdhury, R. V. F. Janssens, and T. L. Khoo)

This experiment investigates the transition between quasi-elastic

reactions, which are strongly dependent on nuclear structure, and deep-

inelastic reactions, which are dominated by statistical features.

Encouraged by a preliminary expe:-iment described last year, a more

extensive experiment was performed where the gamma sum energy, and the

characteristic gamma rays from one and both of the fragments for

345-MeV 5 8Ni + 5 8 Ni were recorded. The analysis is currently underway.

Experiments at other incident energies and involving different target-

projectile combinations are planned.

99

D. ACCELERATOR MASS SPECTROMETRY (AMS)

Over the past few years the technique of AMS has developed into apowerful tool to measure extremely low conce tra ions 10-1 3O 10-15) of a

variet 4 of long-lived radi isotopes (1 Be, C, Al, Si, Cl,Ca Ti, 59Ni, 6 0Fe, 12 I). At present about 20 laboratories throughout

the world (mainly centered around tandem accelerators) are using thistechnique. Most of the laboratories have embarked on rather extensivemeasurements in applied fields (e.g. Geophysics, Hydrology, Archeology,Meteoritics). At Argonne a line more closely rel 9td to6nuclear physics ispursued. At present, measurements on half-lives 44 4 Ti, F 1 , exotic ions(doubly-charged negative), and on the detection of natural Ca areunderway. Both the tandem alone and the tandem-linac system in connectionwith Enge split-pole spectrographs are used. The higher energies from thelinac allow one to extend the measurements to heavier isotopes for betteridentification. In addition, for some cases the very clean separationtechnique of fully-stripped ions.

a. Measurement of the Half-Life of 4 4 Ti via Accelerator MassSpectrometry (D. Frekers, W. Henning, W. Kutschera,K. E. Rehm, R. K. Smither, J. L. Yntema, and B. Stievano*)

The half-life of 4 4 Ti has been measured from the specific

activity using the technique of accelerator mass spectrometry. The

interest in a remeasurement of the half-life arose from the fact that a

previously-performed irradiation of a 45Sc sample with 45-MeV protons had

yielded a substantial amount of 4 4 Ti, which could possibly be used for the

preparation of a target for future experiments. For the present

application of accelerator mass spectrometry, several TiO2 samples, spiked

with 44Ti of about 1.2-pCi total activity, have been prepared and used as

sputter targets for injection of a TiO beam. 44Ti was accelerated to 80

MeV in the FN tandem and identified in the Enge split-pole spectrograph at

6 = 00. The strong and ever present background contributions from

different ion beams with the same magnetic rigidity were effectively

eliminated using a second stripper foil in the spectrograph scattering

chamber and, by means of two movable shields, blocking all but the 15+

charge state from entering the focal-plane detector. A typical AE-E

spectrum obtained during the measurement is shown in Fig. 11-15. The

concentration of 44 Ti in the source material (4 4 Ti/Ti = 2 x 10-7) was

measured with rerpect to the yield of the 4 6Ti isotope. Mass-fractionating

^ifects were taken into account by measuring the relative beam currents of

*Istituto Nazionale di Fisica Nucleare, Legnaro, Italy.

100

ACTIVE SAMPLE

a

Ti

9Ti

=2.0 xO 4 4 .44

47 467

BLANK SAMPLE

44T< I I10

47 4 6 Ti48T 4 4TI

49Ti

44C

("'I'll 111VW

Fig. 11-15. An isometric view of the 2-dimensional AE-E spectrum for theZ % 22 region measured with the focal-plane detector of the magneticspectrograph. The lower part shows the result from a blank sample whereasthe upper part was obtained using a 4 4Ti-spiked sample. The variousbackground components are indicated.

o

4

102

the stable Ti isotopes (46-50Ti) for equal velocities at the terminal

stripper. An overall sensitivity for the 4 4 Ti concentration of 1 x 10-10

was achieved proving accelerator mass spectrometry to be a powerful tool

for radioisotope detection even for heavier elements. Our value for the

half-life of 4 4Ti, 54.2 2.1 y, turns out to be slightly higher than the

previously accepted value of 47.3 0.9 y (see Fig. 11-16).

b. Search for Doubly-Charged Negative Ions via Accelerator MassSpectrometry (W. Kutschera, D. Frekers, R. Pardo, K. E. Rehm,R. K. Smither, and J. L. Yntema)

Doubly-charged negative ions would be highly desirable for tandem

accelerators since the total energy gain of the ion beam could be

substantially increased. The production probability for these exotic ions,

however, is known to be extremely low. We have performed an ultrasensitive

measurement of the production rate of doubly-charged negative ions in a

sputter source using the techniques of accelerator mass spectrometry. If

ions fully stripped at the terminal are selected after acceleration in the

tandem, an unambiguous energy signature can be derived. Setting the beam

transport system to the corresponding rigidities, doubly-charged negative

ions can be identified in the Enge split-pole magnetic spectrograph under

very clean conditions. In our experiment we have focussed on the

investigation of 11B, 12C, and 160. These elements are known to produce

singly-charged negative ions with high probability. Several high-

sensitivity measurements were carried out and no doubly-charged negative

ions were identified at a level of 10-14 to 10-15 (with respect to singly-

charged negative ions). A search for singly-charged negative ions of He

and Ne was also performed. After stripping in the tandem foil, copious

amounts of 4He2+ ions (>103 per sec) were observed, but no signal

from 2 0Ne9 + ions in 30 min. He is known to have a half-life of 15 Iasec

%hich is in the same order of magnitude as the flight time from the ion

source to the terminal. It may therefore be concluded that if

Ne~, 11 B-- 1 2C~ and 160-- do exist, their half-life must be much shorter

than 1 sec or the production probability must be greatly suppressed.

101

I

+-- 54.2 2 .1y

+--- 47.3 0.9 y

456RUN

7 8 9 10

Fig. 11-16. The results of ten different half-life measurements, giving

a mean value of 54.2 2.1 y. The previously accepted value isindicated by the hatched area around 47.3 y.

62

6 0 -

58-

56T

NN~

54

52

50-

AQ

ALLh-T'

2 3

-- x r r y r r y r r y r

ZI&&

to

I

p

i

103

c. Accelerator Mass Spectrometry of lCa (W. Kutschera, D. Frekers,K. E. Rehm. R. K. Smither, J. L. Yntema, Ma Xiuzeng,*and M. Pault)

The goal of this experiment is to detect the long-lived

radioisotope 41Ca(T1 /2 = 1 X 105 yr) at natural concentrations estimated)

to be as low as 41Ca/Ca = 10-15. Since 41Ca is produced in the earth's

crust through thermal neutron capture from cosmic-ray secondary neutrons, a

successful method for 4 1Ca detection would offer numerous geo- and archeo-

chronological applications. In order to reach this goal several problems

have to be solved: 1) the isobaric interference of 41K must be removed, 2)

the background from stable Ca isotopes must be efficiently suppressed, and

3) the yield of negative Ca ions must be greatly increased. The last

problem appears to be the most difficult to solve.

So far the experiments were performed using the tandem

accelerator in conjunction with the Enge split-pole spectrograph as a

highly sensitive mass spectrometer. A schematic layout of the system is

shown in Fig. 11-17. 4 1 Ca/Ca ratios were measured from samples in the ion

source by identifying and counting 91-MeV 4 1 Ca ions in the split-pole

spectrograph and relating this number to a 4 0Ca current measurement in the

split-pole scattering chamber. With a careful consideration of relevant

normalizing parameters absolute ratios with a precision around 10% can be

measured.

The most convenient end product of any preparatory chemistry is

CaO. Therefore we used this material in the ion source. Since Ca does not

like to form negative elemental ions (even from metal Ca) one has to use

molecular ions. In a first run we tried CaO~ ions with little success.

Low yield and interferences from close-lying molecules made a clean

identification of 4 1 Ca impossible. Somewhat better was CaH. However, K

also forms KHi and hence the 4 1 Ca - 4 1K interference is not removed. In

the second run we used CaH3 ~ ions. The output was enhanced by spraying NH 3

onto the CaO samples. Apparently, KH 3 ions do not form in any detectable

quantity which solves the isobaric interference problem completely. This

*Institute of Atomic Energy, Peking, Peoples Republic of China.

tHebrew University, Jerusalem.

1G. M. Raisbeck and F. Yiou, Nature 277, 42 (1979).

104

SPUTTER BEAMEGATIVECTONSOURCE

ISO kV ELECTROSTATICPREACCELERATION QAR

ELECTROSTATICEIN LLENS

FAR ~4

INJECTIMAGNET ELECTROSTATIC

ER X-Y STEERERS

FN TANDEM

9MV

FIELJSTRIPPER

MAGNETIC 90

- QUAD POLE BJCT ANALYZING

FARADAY MA TIC_ CUP X-Y STEERERS

IMAGE SLIT

FARADY

SWITCHIMAC1-T

MAGNETIC

MAGNETICX-Y STE ER

SPLIT - POLEMAGNE TIC

x SPECTROGRAPH .010

Fig. 11-17. Schematic layout of the experimental system used inradioisotope detection with the FN tandem.

105

I I43Ca

ACTIVE SAMPLE

- 41 -Ca =3X0-8 42Ca Ca

10 min.

- Ca

40Ca

CCa-

BLANK SAMPLE

41- C-10-

--- _ 3xIO

- 55 min.-

80ETOTAL

9085(MeV)

Fig. 11-18. Total energy spectra of various Ca isotopesfocal plane detector of the split-pole spectrograph.energy of the ions is approximately 13 MeV lower thandue to the energy loss in the detector entrance foil.

measured in theThe measuredthe incident energy

410

I02

1210

I0

zzQ0

0 2

102

10

I75

i

106

confirms previous findings of Raisbeck et al.2. Figure 11-18 shows total

energy spectra measured for an enriched 4 1Ca material and a blank. Strong

background peaks of 4 3Ca and 42Ca appear because 4 1 CaH3 ~ is injected into

the tandem accepting 4 2 CaH2 and 4 3 CaH ions as well. By multiple charge

changes in the accelerator tubes these ions produce a "white" spectrum of

magnetic rigidities after the tandem from which small bins are cut out by

the purely magnetic transport system set up to accept 4 1 Ca 1G+ ions. An

addition of a Wien filter or an electrostatic separator should greatly

suppress this degeneracy.

40Ca10+ currents of 0.4 nA were measured for normalization. As

can be judged from the results of Fig. 11-18 we have yet to go a long way

to reach the goal of 4 1 Ca/Ca ratios around 10-15. Several approaches will

be tried: 1) Ca metal instead of CaO should yield a factor 100 more output

of CaH3- ions. Although factors of 700 have been measured in our

laboratory in the past, reproducible conditions have not been

established. 2) In order to reach highest sensitivity a background-free

condition must be established. We will try two different approaches. One

is to use a Wien filter for an isotopic cleanup in the present system. The

other is to use the tandem-linac system. Due to the stringent phase-

matching requirements, the linac acts as an excellent mass filter. In

addition, the increased energy after the linac would allow a much cleaner

identification as compared to tandem energies. Assuming an optimistic

increase of a factor 1000 for the Ca current and a background-free

condition, we would be able to measure a 4 1 Ca/Ca ratio of 1 x 10-15 with

one 4 1Ca count per hour. Such a condition has been achieved in several

laboratories for lighter, long-lived radioisotopes (e.g. 3 6C1) which,

however, easily form negative ions.

2G. M. Raisbeck, F. Yiou, A. Peghaire, J. Guillot, and J. Uzureau, Proc.

Symp. on Accel. Mass Spectrometry, Argonne 1981, Argonne Natl. Laboratory

Report ANL/PHY-81-1, p. 426.

107

d. Measurement of the Half-Life of 60Fe Using the Tandem-LinacSystem as an Accelerator Mass Spectrometer (W. Kutschera,P. J. Billquist, D. Frekers, W. Henning, X. Z. Ma,* L. F. Mausner,tM. Paul,* R. Pardo, K.E. Rehm, R. K. Smither,and J. L. Yntema)

The half-life of 6 0 Fe has been measured only once in the past'

yielding a value of T1/2 = 3 x 105 y, uncertain by a factor 3. The

recent finding2 of extinct 26AI activity (T1/2 = 7.2 x 105 y) through the

Allende meteorite makes 60Fe potentially interesting as a possible

signature of iron peak nucleosynthesis. An improved half-life value

for 60Fe could lead to its use as an interesting geo- and

cosmochronological tracer in the million-year range. In particular, a

measurement of 60Fe in meteorites3 with the highly-sensitive method of

Accelerator Mass Spectrometry (AMS) seems feasible.

We are presently engaged in an experiment to improve the accuracy

in the half-life value of 60Fe by measuring both the amount of 60Fe nuclei

and the decay rate of a spallation-produced sample using the relation

dN/dt = -AN. The sample material was produced by irradition of 4.5 g/cm2

Cu with 18.7 mAh of 193-MeV protons in the Brookhaven Linac Isotope

Producer (BLIP). Onc year after irradiation the iron fraction was

chemically extracted. This material contained approximately 1015 6 0Fe

nuclei besides mCi quantities of 5 5Fe (T1/2 = 2.7 y) and pCi amounts

of 5 9 Fe(T1 / 2 = 43.1 d). After an additional period of 5 months, the 6 0Fe

content was determined by adding a known amount of stable iron (>100 times

the original amount) and measuring the 60Fe/Fe ratio with AMS. For this

measurement several 130-mg Fe pellets were put into an improved inverted

*Institute of Atomic Energy, Peking, Peoples Republic of China.

tBrookhaven National Laboratory, Long Island, New York.

*The Hebrew University of Jerusalem, Jerusalem, Israel.

1J.-C. Roy and T. P. Kohman, Can. J. Phys. 35, 649 (1957).2T. Lee, D. A. Papanastassiou and G. J. Wasserburg, Geophys. Res. Lett.

3 109 (1976); Astrophys. J. 211, L107 (1977).

'P.S. Goel and M. Honda, J. Geophys. Res. 70, 747 (1965).

108

60Ni

xl

6Fe

ACTIVE Fe

300 6Fe/min60 Fe /Fe=1.2x 07

BLANK Fe

1.2 60Fe/min

6 0Fe/Fe = -9. x0

60.

F

60Fe /mi n

Cu

0. I

x0060F

aF ET Fe

Fig. 11-19. Isometric plot of energy loss, AE, vs. total energy signals,ET, measured in the focal-plane detector of the split-polespectrograph. All three dimensions are linear with the vertical scalevarying as indicated.

xIO

w

/a

1

wl

109//C

sputter source. 4 The tandem-linac system accelerated the mass-60 ions to

360 MeV and these were detected using and Enge split-pole magnetic

spectrograph. A strong 60Ni background cmponent following 6 0 Fe through the

entire acceleration process was separated by the difference in energy loss

in a 2.8 mg/cm2 thick Al foil stack. The subsequent position splitting in

the focal plane of the spectrograph allowed a physical shielding of the

main Ni component fromthe focal-plane detector. The resulting energy

spectrum measured with an ionization-type detector io shown in

Fig. 11-19. The 6 0 Fe/Fe ratios were obtained by normalizing to the 56Fe

current measured at the entrance of the linac. From 18 individual runs on

two active pellets, a 60Fe/Fe ratio of 1.16 x 10-7 with an uncertainty of

20% was determined. The relatively large uncertainty is due to systematic

errors in measuring an absolute ratio with such a highly complex system.

At present we are measuring the (slow) grow-in of the 6 0Co gamma-ray

activity (T 1 / 2 = 5.27 y, EY = 1.332 MeV). From preliminary values of this

measurement and the 6 0 Fe/Fe ratio we find that T1/2 Z 4 X 105y.

The 6 0 Fe/Fe ratio measurement has shown that AMS experiments can

be performed with the tandem'-linac system in the mass-60 range. An

extension to heavier radioisotopes seems possible, in particular when the

completed ATLAS system will provide heavy-ion beams pproaching 1 GeV.

Although combined accelerator systems beconw highly complex devices for

quantitative mass spectrometry, the current trend of steadily increasing

computer-assisted accelerator control may well make this type of

measurement more feasible in the future.

4J. L. Yntema and P. J. Billquist, Nucl. Instrum. Methods 199, 637

(1982)

111

E. SELECTED NUCLEAR SPECTROSCOPY AT THE TANDEM-LINAC

In addition to the programs described above, there are otheractivities at the tandem-linac. The main one involves on-line laserspectroscopy which has been initiated recently. The optical hyperfinestructure of radioactive atoms will be studied, in order to extractinformation on spins, moments, and the variation of charge radii for groundstates and isomers. The laser system has been installed and tests of thecryogenic helium jet which transports the atoms into the interaction regionhave been completed. Work is now proceeding on coupling the laser systemto the cryogenic helium jet. There has also been a search for a transientelectric field gradient acting on ions slowing down ig a solid.Measurements have also been performed on the? Be(p,Y) B r action, which isof astrophysical interest, of resonances in Be(a,Y) and Li(a'Y) and ofthe Be decay branching ratio.

a. Laser Spectroscopy of Radioactive Atoms (C. N. Davids,D. A. Lewis,* R. Evans,* M. A. Finn,t G. Greenlees,tand S. L. Kaufmant)

The linac target station for the cryogenic helium jet has been

completed. Tests using the linac beam have been conducted, indicating

copious production of Ba radionuclides using the 12 2 Sn(12C,xn)1 3 4-xBa

reactions. The skimmer efficiency for Ba is 2.5%, slightly higher than

that obtained for lighter As, Ge, and Ga isotopes. This is expected since

the opening cone angle at the capillary varies as M-1/2, where M is the

mass of the species. A large blower pump has been installed, and is

expected to produce a better vacuum in the helium exhaust chamber. This in

turn should lead td'better cooling of the atomic beam upon emergence from

the capillary.

The laser beam transport system between the laser laboratory and

the cryogenic helium jet has been installed. Tests to reduce the laser

light scattering background will begin soon.

Work with the stable atomic beam chamber has shown that the laser

line width is 7 MHz. This is quite adequate for the isotope shift

measurements. The light collection efficiency of the elliptical cylinder

light collector has been measured using a line filament light bulb. It

agrees with calculations, and should lead to a high overall efficiency for

detecting bursts of photons emitted by the excited atoms.

*Iowa State University, Ames, Iowa.

tUniversity of Minnesota, Minneapolis, Minnesota.

112

A data-acquisition system consisting of an LSI-1l/02

minicomputer, floppy disk drive, terminal, and CAMAC hardware has been

assembled. This system enables spectra of burst multiplicity to be

recorded. In addition, the computer controls the scanning of the dye-laser

frequency in precise steps.

b. Search for Transient Electric Field Gradient Acting onFast-Moving Ions in Solids (H. Ernst, W. Henning,T. J. Humanic, T. L. Khoo, S. C. Pieper, and J. P. Schiffer)

As a fast ion slows down in a solid the transient electric field

acting on it should give rise to a field gradient at the nucleus. Such a

field should interact with the quadrupole moment of the moving nucleus and

cause a perturbation in the angular correlation of the emitted Y rays. If

the gradient is sufficiently large it could be utilized as a powerful test

for measuring the quadrupole moments of states with lifetimes as short as a

few picoseconds. In our experiment we searched for a perturbation in the

angular correlation of Y rays deexciting the 2+ states of 56Fe and 24Mg,

which were both Coulomb-excited in the bombardment of 24Mg with 125-

MeV 5 6 Fe beams from the linac. No effect was detected within experimental

limits and an upper limit of 1021 V cm-2 was set for the electric field

gradient. A paper has been published in Physical Review on the results.

c. The 7 Be(p,Y) 8 B Reaction (B. Filippone,* A. J. Elwyn, C. N. Davids,D. Koetke,t and W. Ray, Jr.)

The 7 Be(p,Y)8B reaction has been measured from Ecm = 117--1230

keV by detecting the delayed a particles from the 8B 0 decay. The

occurrence of this reaction in the sun produces high-energy neutrinos which

account for nearly 80% of the neutrino capture rate in the 37C1 solar

neutrino experiment.

A 7Be radioactive target (t1/2 = 53.3 days) of 80 mCi was

produced by a high-voltage electroplating technique in an organic

solution. The 7Be was produced via the 7 Li(p,n) 7 Be reaction and then

chemically separated from the 7 Li and purified.

*Thesis Student, University of Chicago, Chicago, Illinois.

tValparaiso University, Valparaiso, Indiana.

113

10 :-

-i 2

b

10 ---

I0

0 400 800 1200Ec.m.(keV)

Fig. 11-20. Total cross section for the reaction Be(p,y)8B as a function

of the center-of-mass energy. The solid curve is the cross sectioncalculated from the theoretical s-factors of Ref. 1, normalized to the

data.

1T.A. Tombrello, Nucl. Phys. 71, 459 (1965).

114

The 7Li(d,p)8Li and 7Li(p,Y)8Be reactions were used to analyze

the target characteristics (from the 7 Li built up from7Be decay) along

with a Pb- collimated NaI detector which scanned the T-ray activity of the

target.

Figure 11-20 shows the measured total cross section as a function

of center-of-mass energy. The extracted astrophysical S-factor from the

present experiment is S17(0) = 0.0216 0.0025 keV-b. This value lowers

the predicted solar neutrino capture rate in the 37C1 experiment by ^25%.

d. Resonances in 7Be(aY) and 7Li(a,y) (A. J. Elwyn, B. Filippone,*G. Hardie,t R. E. Segel,* and M. Wiescher )

A target containing about 80 m Ci (2 x 101 6 atoms) of 7 Be was

bombarded by alpha particles from the Argonne Dynamitron with the capture

gamma rays detected by ? large NaI(T2) crystal and by a Ge(Li)

spectrometer. The detector efficiences were obtained by measuring the

spectrum from the 992-keV 2 2 A1(p,y) resonance. From the thick-target

yields 7Be(a,y) resonance strengths wr = (0.34 f 0.07) eV and (4.45 1.2)

eV were found for the 880-keV and the 1380-keV resonances, respectively.

It is apparently the first time that these yields have been measured. For

the 7Li(a,y) reaction preliminary analysis yields wL = 0.012 eV, 0.54 eV,

and 1.95 eV for the 401-keV, 820-keV, and 958-keV resonances,

respectively. The value for the 820-keV resonance is in good agreement

with that given in the compilation but the previously accepted values for

the other two resonances are considerably higher. Reasons for accepting

the present values will be given. Branching ratio data were obtained for

all the resonances and the individual radiative widths show some agreement,

and some disagreement, with theoretical predictions.

*Thesis student, University of Chicago, Chicago, Illinois.

tWestern Michigan University, Kalamazoo, Michigan.


Ohio State University, Columbus, Ohio.

115

e. The 7 Be Decay Branching Radio (C. N. Davids, A. J. Elwyn,B. W. Filippone, S. B. Kaufman,* K. E. Rehm, and J. P. Schiffer)

The branching ratio for the electron capture decay of 7Be to the

first excited state in 7Li is an important number in astrophysics. The

currently accepted value for the branch...ng ratio is 10.37 * 0.12%, but a

recent preprint by Rolfs et al. reports a value of 15.4 * 0.8%. We have

measured the branching ratio by implanting 89.04 x 106 7Be nuclei in a Si

surface barrier detector and subsequently counting the 478-keV decay Y rays

in a well-shielded Ge(Li) detector. The Be nuclei were produced via

the 1H(7Li, Be)n reaction at 15.5-MeV bombarding energy, and were allowed

to recoil into an Enge split-pole spectrograph placed at 1.60 to the

incident beam. A clean separation of 7 Be from contaminants allowed

placement of the Si detector in the magnet focal plane, and an analysis of

the energy spectrum in the detector yielded the total number of 7 Be

nuclei. Figure 11-21 shows the energy spectrum for one of the runs lasting

about 40 minutes. The resulting branching ratio is 10.61 f 0.23%, which

agrees with the currently accepted value.


116

' I I

123+

\C

7.2+Li- 9

4H

IB3+ 1

200I 0

' I

SCATTERED7 .3+

PULSER

/i14N4+ 17 5+

1I4+B4 B 14N5+

e3+ 9Be4+2+e

I706+

12C5+

04 1605+ 1505+

i I400 600 800 1000

CHANNEL NUMBER

Fig. 11-21. Energy spectrum in Si detector mounted in the focal plane ofthe Enge split-pole spectrograph. The double peak marked "Li isdue to slit-edge scattered beam particles. Other identified peaks aredue to 7Li-induced reactions on Li and 12C.

' I

Be

' I

4N6+

10

10

-JzzI0

C!)Fz00

l03

210

10

-

| 1 ls -L

117

F. EQUIPMENT DEVELOPMENT AT THE TANDEM-L INAC FACILITY

The experimental areas of the linac are now reachingcompletion. The Enge spectrograph is operational on a routine basis, andsignificant improvements have been made to its focal-plane detector. The65" scattering- chamber has been continually upgraded primarily to permitmore refined operation with longer flight paths. Detectors have beendeveloped for efficient detection of heavy evaporation residues and topermit high resolution time-of-flight measurements. A new beam line hasbeen installed with two target stations. One has a thin-walled Al chamberfor neutron time-of-flight measurements and the other incorporates anupgraded Y-ray facility. A plunger which fits inside the sum spectrometerhas been extensively tested and used successfully in several experiments.A general-purpose beam line has been installed and used in several atomicphysics experiments, while a beam line for a superconducting- spectrometeris almost complete. Effort has also been devoted to planning for the ATLASfacility. This activity is described elsewhere in this document.

a. Ray-Tracing Corrections for the Focal-Plane Counterat the Spectrograph (K. E. Rehm)

Reactions between two medium-weight nuclei usually show a large

kinematical shift. For experiments with the split-pole spectrograph this

implies that the detector has to be moved very close towards the exit of

the magnet, which is not possible for many cases due to mechanical

reasons. It is, however, possible to reconstruct by ray-tracing techniques

the actual focal plane from two position measurements taken outside the

focal plane. From our measurements with two position wires, separated by

50 mm, we have obtained energy resolutions of ~1 x 10-3 after the ray-

tracing correction. An example of the reconstruction of the actual focal

plane is shown in Fig-. 11-22 for the case of elastic scattering- of 50-

MeV 160 on 27Al at blab - 200. The same technique can also be used to

correct the angle dependence of the AE signal. This strongly improves the

Z resolution for heavy-ion reactions at large solid angles. Ray-tracing

corrections are also of importance in future experiments with the split-

pole spectrograph at the ATLAS accelerator. Presently we are working on

the implementation of the ray-tracing correction into the on-line data-

acquisition program.

FOCAL PLANEWIRE IWIRE 2

0 400 800 1200 1600 2000

480 Bp SPECMEASUREWIRE I

TRUMD A

Bp SECTRM CLCUAE

320E

1601

200-

160-

1201-

801-

40

Bp SPECTRUM CALCULATED

FOR ACTUAL FOCAL PLANE

420 460 500 540 580CHANNEL NUMBER

Fig. I1-22. Reconstruction of the actual focal plameasurements.

620

ne using two position

118

1500

1000

500k

-JUzzI<-)

U)

I-zD0U-

500 540 580 620 660 700

20001

ir-I 1 1 md&

VIA l u

119

b . Test of the Large Focal-Plane Counter for the Linac MagneticSpectrograph (K. E. Rehm, W. Kutschera, and D. G. Kovar)

Experiments with high-energetic (~10-MeV/nucleon) heavy ions in

the magnetic spectrograph require large focal-plane detectors with good

resolutions to identify the detected particles. We have thoroughly tested

a 25-cm deep position-sensitive ionization chamber with 160, 37Cl and 5 8Ni

ions. This detector is now used routinely for experiments at the linac

spectrograph. Resolutions obtained with 150-MeV 160 ions were: QE : 2.9%,

E : 0.75%, position : 1 mm. The improvements in the QE and E resolution

are mainly due to the use of CF4 as counter gas, which has the additional

advantage of being nonflammable. This allows us to study nuclear reactions

between medium-weight nuclei on heavy targets with better resolution than

hitherto possible. We are planning to add a parallel-plate avalanche

counter to the present system for time-of-flight information to improve the

mass resolution for experiments with projectiles in the A = 100 region.

c. A AE-E Detector for Fusion Measurements (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, W. KuYhn, J. P. Schiffer,and B. Zeidman)

An improved AE-E detector has been constructed for identifying

evaporation residues from heavy-ion fusion reactions. The detector

consists of four silicon surface-barrier detectors (450 mm2 x 300 u thick)

placed inside a AE gas-filled ionization chamber. The back plate on which

the silicon detectors are mounted may be easily removed and replaced with

another plate whose design and function is at the user's discretion. The

maximum available gas volume of the ionization chamber is 19 mm height x

152 mm length x 60 mm deep, and provision is made for installing a grid to

support thin windows (100 pg/cm2). The detector has been used

successfully in conjunction with an electrostatic deflector to measure

evaporation-residue angular distributions for several moderately heavy

systems (AN~ 180). In the course of these measurements, the limitations

of the AE-E method for detecting and identifying very heavy, low-energy

evaporation residues has become apparent. In the future we plan to

incorporate time-of-flight measurements into the system as an additional

means of identification.

120

d. Modifications to the 65" Scattering Chamber For LongFlight-Path Measurements (D. G. Kovar, R. Nielsen, and G. Rosner)

Modifications to the 65" scattering chamber have been made to

allow for x1.5 meter flight paths for time-of-flight measurements. A new

target position was installed at the entrance of the chamber with a

collapsible movable arm attached to the new target position and an existing

ring in the chamber. As the ring is rotated in the angular range 00 to

1000 the new arm rotates from 00 to 550 and the flight path varies from

41.5 to 1 meter. A target holder with eleven target positions has been

installed for measurements. This configuration has been used in

measurements using two micro-channel detector systems plus a Si detector

and masses of "55 amu have been resolved in studies of evaporation

residues. Further modifications to allow for coincidence measurements

using the new target position are planned.

e. The Y-ray Facility (P. Chowdhury, W. Evans, H. Emling,*R. V. F. Janssens, T. L. Khoo, and J. Worthington)

The Y-ray facility has been moved to another location in the new

linac target area annex. As a consequence there is now more space around

the target for large NaI detectors or for neutron time-of-flight

measurements, thereby alleviating the congestion in the previous

location. Improvements to the vacuum system and beam-diagnostics have also

been made.

Extensive tests of a plunger for recoil-distance measurements

have been conducted. The plunger incorporates several unique features,

among them the support of the catcher foil on 3 independent push rods and

the use of a microcomputer to control the rods. Tests have demonstrated

that the position of the catcher foil as given by the microcomputer is

accurate to within 1 in. In addition, a new algorithm has been developed

for quick remote adjustments to achieve parallelism between target and

catcher foils. Measurements of state and feeding times as a function of Y-

sum energy have been performed in 1 5 2, 1 5 4Dy, as described in sections A.c.

and A.f. Future experiments will include similar measurements

*GSI, Darmstadt, W. Germany.

121

in 1 4 7Gd, where we have identified yrast states to the highest spins known,

in 1 8 6Hg, and in some light Re isotopes. In the latter cases the core is

soft toward deformation: lifetimes will provide important information on

the deformation parameters and on their changes with spin.

Design studies are currently being undertaken for a facility

consisting of (a) a sum-energy/multiplicity analyzer consisting of 60

bismuth germanate (BGO) detectors and (b) an array of 7 anti-Compton

spectrometers, where BGO is used for detecting Y-rays which are Compton-

scattered out of the Ge detector. The anti-Compton array will be arranged

outside the sum-energy/multiplicity analyzer. Such a device will enable

the nucleus to be probed to higher spins than has hitherto been possible

with any existing detector systems. The sum energy/multiplicity filter

will also provide valuable data in the study of reaction mechanisms.

f. Superconducting Solenoid Lens Electron Spectrometer (P. J. Daly,*Z. Grabowski,* W. Evans, R. V. F. Janssens, T. L. Khoo,and J. Worthington)

Work has continued for the construction of the Purdue

superconducting electron spectrometer to be installed at the linac. The

coils were delivered by the middle of the year. Field mappings were

performed. They show that the original design goals are met and even

exceeded. No particular problems were encountered in realizing the high

magnetic fields.

Meanwhile, the beam-line design has been finalized at Argonne and

construction has started. First studies of the beam quality through the

line are expected in spring 1983. The installation of the spectrometer

should take place before the end of the year. A variety of experiments is

planned, some of which will take advantage of the possibility of measuring

e--e- coincidences.


122

g. General-Purpose Beam Line

A general-purpose beam line has been constructed to which

equipment may be attached for limited time intervals. Outside users or

those with no facilities at the present permanent stations will be able to

take advantage of this facility. It has already been used in several

atomic physics experiments.

The target system for atomic physics experiments will include a

scattering clamber for ion-atom and ion-foil collisions. Such a chamber

(diameter 140 cm) would be attached to a high-resolution electron

spectrometer, and also be used for Coulomb-explosion experiments involving

charged-particle detection. A second target chamber further downbeam will

be available for photon spectroscopy measurements of ion-atom and ion-foil

collisions. Pumping systems will include two turbo-molecular pumps and an

ion pump.

h. Nuclear Target Making and Development (G. E. Thomas)

The Physics Division has a facility which is used principally to

produce very thin films for experiments at the Tandem-Linac and Dynamitron

accelerators as well as for experiments of other members of the Division.

In addition, it is available to any other division at the Laboratory

needing this service and occasionally to other laboratories and

universities.

This year we again produced targets varying in thickness from a

few monolayers to several mg/cm2. The different elements, isotopes, or

compounds evaporated or rolled included the following: Au, Al, BaF2 ,10,11,normalB, Bi, C, 4 Ca, CH2' 155,156Gd, 76Ge, K, 6,7,normalLiF,

LiH, Li, 24,26,normalMg, gF2, 92,94,95Mo, 58, 62Nc, 206,208,normalPb,96Ru,112 ,114 ,116 ,118 ,120 ,122 ,124Sn, 28,29,30,normals5 , 1 25Te, and92 ,94Zn.

Methods have been developed to better produce the more complex

targets made for experiments at the heavy-ion facility. One such type is a

"sandwich" produced by evaporating an absorber material (15 mg/cm-2 ) onto a

rolled separated isotope target (1 mg/cm- 2 ) or the target (1 mg/cm- 2 ) may

123

be evaporated onto the rolled absorber material (15 mg/cm- 2 ). Another type

is produced by evaporating the separated isotope (1 mg/cm 2 ) onto a very

tightly and smoothly stretched Au (1 mg/cm- 2 ) foil. "Sandwich" targets

produced by the above methods include 1 5 5 , 1 5 6 Gd + Pb, 1 5 6 Gd + Bi +

Pb, 92,94,95Mo+Pb,b58,62Ni + Pb, 122,124Sn + Au, 12 5Te + Pb, and 9 2 , 9 4 Zr

+ Pb.

New systems being developed for the facility include a

computerized target-storage system using turbo-pumps (work in collaboration

with J. N. Worthington and B. G. Nardi), a system for producing targets

using a new type of sputter source, and a clean evaporator system using a

cryo-pump. Plans for the future also include building a new type of multi-

target evaporator system using a rotating wheel. A continuing objective is

to improve target quality.

1251P6

III. THEORETICAL NUCLEAR PHYSICS

Introduction

The principal areas of research in the nuclear theory programare:

1. Nuclear forces and sub-nucleon degrees of freedom.2. Variational calculations of finIte many-body systems.3. Nuclear shell theory and nuclear structure.4. Intermediate energy physics with pions, electrons and nucleons.5. Heavy-ion interactions.

In 1983 encouraging results were found for the strong couplingapp oximation to the static chiral bag model of the nucleon. The treatmentof He, including 3-body forces, was extended to several excited stateswith good results. The nuclear structure calculations of the effects of A

admixture obtained a striking result, namely that in simple nucleisuppression of M1 matrix elements is much stronger for nondiagonal casesthan for diagonal cases like magnetic moments, in agreement withobservation. Consideration of possible experiments with a GeV electronaccelerator was stimulated by a series of lectures given by visitingArgonne Fellow, J. Dirk Walecka.

127

A. NUCLEAR FORCES AND SUBNUCLEON DEGREES OF FREEDOM

F. Coester, B. D. Day, T.-S. H. Lee, J. Parmentola,R. Wiringa, and collaborators from other institutions

Much of our work is motivated by three central questions. (1)What should be the active degrees of freedom? (2) What is the Hamiltonianthat governs the nuclear many-body dynamics? (3) What can electromagneticprobes reveal about short-distance nuclear structure?

For the conventional nuclear theory which assumes that nucleonsare the only active degrees of freedom it is not required that two-bodyforces alone are sufficient, but it is essential that the same Hamiltonianaccount for both light and heavy nuclei and that the importance of the n-body forces decrease rapidly with increasing n. We have previouslyestablished that two-body forces alone cannot account for the properties ofnuclear matter. During 1981-833we investigated the effects of severalthree-body interactions in H, He, He and nuclear matter. Inclusion ofthese three-body forces is a marked improvement, but open questions remain.

A promising extension of the conventional theory includes the Aisobar among the active degrees of freedom. This step may drasticallyreduce the need for explicit three-body forces. We have constructed arealistic two-body potential with NA interactions. We expect that adetailed comparison of the properties of different models will lead to abetter understanding of three-body forces and the role of isobars.

The role of quark degrees of freedom in nuclear theory dependscritically on the quark distribution within the nucleon. The assumption ofa "little" quark bag surrounded by a pion (or qq) cloud leaves room formuch of the conventional meson-nucleon dynamics. However, in such modelsthe pion cloud strongly contributes to the structure of the nucleon and anaccurate solution of the one-nucleon problem is a prerequisite for furtherapplications. We have been investigating properties of static chiral bagmodels in the strong coupling approximation.

Constituent quark models with QCD based potentials also predict asmall radius of the constituent quark distribution. Such models accountwell for the spectroscopy of single hadrons, but in their present form theydo not provide a satisfactory multi-hadron dynamics. Along these lines weare working on the development of models designed to include meson creationand hadron-hadron interactions in a satisfactory manner.

Much of the quantitative information that will determine thesuccess or failure of competing models will come from electromagneticprobes. Observed quantities are directly related to matrix elements of theelectric charge and current densities. Probes of short range featuresinevitably involve relativistic effects. A valid interpretation requiresmutually consistent representations of the current operators and the targetwave functions. Work is in progress on the construction of relativisticcurrent operators that are consistent with relativistic particle models.

128

a. Three-Body Forces in Light Nuclei and Nuclear Matter(R. B. Wiringa, J. Carlson* and V. R. Pandharipande*)

Realistic models of three-nucleon interaction (TNI) have been

examined in 3H, 3He, and 4He nuclei, and in nuclear matter. Two-nucleon

potentials that fit NN scattering data, such as Reid, Paris, and

Urbana-v14 , consistently underbind the light nuclei while overbinding-

nuclear matter at too high saturation density. The addition of TNI to the

many-body Hamiltonian can significantly lessen this problem. The Tucson

and isoba. intermediate-state models of the two-pion-exchange potential

(V2w3N) were studied along with an intermediate-range three-nucleon

repulsion (V 3 NR). The Urbana-v1 4 model was used for the two-body force,

and variational upper bounds were calculated for the full Hamiltonian.

Energy expectation values were evaluated by Monte Carlo sampling in the

light nuclei, and with Fermi-hypernetted-chain techniques in nuclear

matter. The nuclear matter calculations are the first to treat TNI without

an "effective" two-body potential approximation.

The realistic TNI bring- theory closer to experiment by giving

extra binding- to the light nuclei and reducing- the saturation density of

nuclear matter. For example, one model with V2n3N and V 3 NR changes the

two-nucleon Urbana-v1 4 results from -7.2 MeV to -8.1 MeV in 3H, and from

-25 MeV to -29 MeV in 4 He (experimental values are -8.48 MeV and -28.3 MeV,

respectively), while the saturation energy in matter is changed from -20

MeV at p = 0.38 fm- 3 to -14 MeV at p = 0.21 fm 3 (empirical value is -16

MeV at p = 0.16 fm-3 ). The Coulomb energy of 3He and the rms charge radii

of the light nuclei are also well described. However the charge form

factors are not close to experiment, probably due to meson-exchange

currents. A paper covering- this work will be published shortly in Nuclear

Phy ics.

We have extended our studies to the lowest-lying- excited states

of 4 He, which include a 0+ breathing mode at 20.1 MeV excitation and 0 and

2 p-wave resonances at 21.1 and 22.1 MeV. These states are unstable

against breakup into p + 3H or n +3 He. A modification of our variational

Monte Carlo method suitable for such unconfined states is used. For the

Hamiltonian mentioned above we find upper bounds for these three excited

*University of Illinois, Urbana, Illinois.

129

2+,0

I-,0

0 -, I

4

2

0

-2

- 2-,0

0-,0

- 040

- 0*90

2-,0

0-,0

d+ 2 H

o-,o

+3 He-- -p + 3H

0+,0

Fig. III-l. Excited states of 4He: the columns show the experimentalspectrum, a Coulomb-corrected spectrum with estimates for theCoulomb energy removed, and the corresponding calculatedspectrum.

2-,I

-4H

-6

- 8

-281

-30

o*,o

0o,0

J 11T Coulomb CalculationEXPT Corrected

"Expt "

130

states at 21.3, 23.6 and 26.8 MeV, with the correct ordering, about 5--20%

above the experimental values (see Fig.III-1). A separate paper covering

this work has been submitted to Nuclear Physics.

b. Present Status of the Nuclear Saturation Problem (B. D. Day)

A basic question in nuclear physics is how nuclear binding

energies and radii, e.e., saturation properties, follow from the

interactions among the constituents of the nucleus. Ultimately this should

be understood in terms of quarks and gluons. At present the most

fundamental treatment for which reliable calculations are possible takes

the nucleus to consist of nucleons interacting through potentials. The

two-body potential is required to fit nucleon-nucleon scattering data up to

350 MeV and to be consistent with our understanding of particle physics,

the most important requirement of the latter type being an OPEP tail.

Coupled-cluster calculations at Argonne and Bochum, and variational

calculations at Urbana and Argonne, have shown that two-body potentials are

inadequate: in most cases they give too high a saturation density for

nuclear matter and substantially underbind light nuclei. Therefore, recent

variational calculations by an Argonne-Urbana group have included three-

body potentials. Roughly 80% of the discrepancies can be removed by

including a three-body force that is repulsive at short range and

attractive at long range. The calculated saturation point in nuclear

matter is at a density about 10% too high, with about 1 MeV per particle

too little binding. If the binding energy of 3H is fitted, then 4He is

overbound by 1--2 MeV. The great improvement means that further work with

three-body forces is essential. A paper giving an overview of the present

situation has been accepted for publication in Comments on Nuclear and

Particle Physics.

c. Studies of Three-Body Forces and Isobar Degrees of Freedom inNuclear Systems (R. B. Wiringa)

The effect of three-body forces in light nuclei, nuclear and

neutron matter is being studied with both phenomenological three-nucleon

potentials and interaction models that explicitly include isobar degrees of

131

freedom. The interplay between two- and three-body forces has been studied

by repeating the calculations with phenomenological three-nucleon

interaction (TNI) described above with a different two-body force, Argonne-

v1 4 (see below). Argonne-v14 has a 6.1% deuteron D state which induces

stronger tensor correlations than the Urbana-v1 4 model's 5.2% D state.

Consistent with the lore of tensor forces in nuclear systems, Argonne-v1 4alone gives less binding, but when TNI is added it actually gives a little

more, due to the attractive combination of the two-pion exchange potential

V2n3N and strong tensor correlation. The results of calculations for light

nuclei are shown in Table III-1 and for nuclear matter in Fig. 11-2. A

paper on this work has been accepted for publication in Nuclear Physics.

Calculations of neutron matter are now in progress. Comparison

of nuclear and neutron matter energies at the empirical saturation density

of nuclear matter, p0, yields a symmetry energy for the Argonne-v1 4 + TNI

Hamiltonian of 30 MeV, of which ~-10% comes from the TNI. This is in

reasonable agreement with semiempirical mass formulae which typically give

30--38 MeV. The equation of state for neutron matter will be used as input

for neutron star calculations to see the effect of TNI on star structure.

It should be dramatic, since the TNI are repulsive here and begin to

dominate the energy around 2p0. This will give a stiffer equation of state

than for two-body forces alone, and a consequent larger maximum star

mass. It will also have implications for supernovae models.

There is now a dispute over the contribution of TNI in the

triton. Two Faddeev calculations in momentum space have now been done by

other groups using the Tucson model TNI, and both get about zero net

contribution. Since our variational calculations give '-1 MeV and should

be rigorous upper bounds, there is a serious discrepancy here. Assuming

there are no bugs in the variational codes, it would indicate that channels

not normally used in Faddeev triton calculations have a large effect on the

TNI contribution. One way to check this is to take the Faddeev wave

functions and calculate expectation values with Monte Carlo methods. The

Los Alamos Faddeev group has offered to provide the wave functions and we

hope to make this calculation in the near future.

An alternative to the phenomenological TNI is to construct two-

body potentials with both nucleon and isobar degrees of freedom. In a

132

Table III-1. Properties of light nuclei with Argonne v1 4 (Urbana

v1 4 ) two-nucleon potential and different three-nucleon potentials: model V

with isobar intermediate-state two-pion-exchange plus repulsive terms and

Tucson two-pion-exchange model. Terms in brackets < > give expectation

values for two- and three-nucleon potentials, while E-V and E-Tucson give

total energies.

3 He 3H 4 He

kinetic 48.8 (44.6) 51.1 (46.5) 109.3 (103.6)

<v14> -55.6 (-51.8) -57.9 (-53.5) -132 (-127.3)

Coulomb .69 .69) 0 (0) .77 (.78)

(Vijk>V - 1.37 (-.97) -1.47 (-1.06) -7.49 (-6.23)

<Vijk>Tucson - 1.28 (-1.02) -1.33 (-1.09) -7.69 (-6.48)

E-V - 7.5 .l(-7.4 .l) -8.2 .l(-8.1 .1) -29.6 .4(-29.l .4)

E-Tucson - 7.4 .l(-7.4 .l) -8.1 .1(-8.1 .1) -29.8 .5(-29.3 .5)

E-expt. - 7.72 -8.48 -28.3

<r2>1/2 -calc. 1.82 (1.86) 1.73 (1.76) 1.62 (1.63)

<r2>/ 2 -expt. 1.84 .05 1.70 .05 1.67 .03

133

*1' I ' I ' ' -- - I ' -

-10 S

EMPIRICAL

v14-20 - -

ARGONNE----- URBANA TUCSON

-.0 1.2 1.4 1.6 1.8 2.0-I

kF(fm

Fig. 111-2. Nuclear matter energy: curves labeled "v1 4 "', "V" and"Tucson" show results with Argonne v 1 4 and Urbana v14 two-nucleonpotentials alone, with model V, and with Tucson model three-nucleonpotentials, respectively.

134

many-body environment many of the processes contributing to the three-body

forces will then be automatically incorporated as soon as three-body

clusters are considered. Fermi-hypernetted-chain techniques for

variational calculations of nuclear matter with such potentials have been

developed previously. However the available published potentials of this

type have a variety of deficiences, so we have concentrated on building a

more reliable potential with NA interactions (see below). This potential,

Argonne-v2 8 , has now been completed and we plan to return to the nuclear

matter calculations in the near future. We hope that detailed comparisons

of nuclear systems with Argonne-v14 + phenomenological TNI versus Argonne-

v28 will lead to a better understanding of three-body forces and the role

of isobars.

d. Nucleon-Nucleon Potentials with Isobars (R. B. Wiringa, R. A.Smith,* and T. Ainswortht)

An NN potential model called Argonne-v 2 8 that includes NN-NA and

NN-AA transitions has been constructed. The intermediate-range attraction

observed in NN scattering can be attributed largely to two-pion-exchange

processes with possible isobars in the intermediate state. Part of these

processes behaves like a twice-iterated one-pion-exchange potential with

NA coupling. The description of many physical processes, where isobars

are believed to play an important role, will benefit greatly from reliable

NA transition models with good fits to the scattering data.

In present work, the isobar is treated as a stable particle. A

one-pion-exchange potential, containing 1NN, iNA, and iAA couplings is

supplemented by phenomenological intermediate and short-range terms. The

NN-NN part is taken in a v1 4 form, i.e., fourteen operator components, and

with the transitions added, a total of 28 operators appear in the full

potential. The coupled-channel Schr6dinger equation is solved for the

deuteron and all J45 partial waves in the NN channel for a variety of

energies up to 400 MeV. This includes up to twelve coupled channels in

the 3 F4 - 3 H4 component. The phenomenological part of the potential is

*Texas A & M University, College Station, Texas.

tState University of New York, Stony Brook, New York.

135

I.i

150- -c

I,0

100 .

0,

-50-

-100- -- '-

0 0.5 1.0 1.5 2.0

r (fm)

Fig. 111-3. Effect of coupling NN to NW and WW channels on the S0, T-1central (vc) and '2(vq)NN potentials: dashed line shows v1 4 modelwith no coupling, dotted line a model with coupling to NW channels,

and solid line the v 2 8 model with coupling to NW and WW channels.

adjusted to obtain good fits to np phase shifts. A direct comparison to

1760 np data points in the range 5--330 MeV shows an excellent fit with a

x2/point of 1.70. Deuteron properties are also well reproduced.

As an exercise in learning how to efficiently search in a large

parameter space for the best fit, the code was also used to construct a

conventional NN potential, Argonne-v1 4 . This potential was built with the

same structure as the Urbana-v1 4 model, for which reliable variational

many-body calculations have been developed. It has already been used in a

study of phenomenological three-body forces (see above). It also gives an

excellent fit to data, and has a similar structure to the v2 8 model to

facilitate comparison of results from many-body calculations. A comparison

of the v1 4 and v2 8 potentials in NN S-0, T-1 channels is shown in Fig. III-

136

3. Because of the effective attraction provided by coupling to NA and AA

intermediate states there is significantly less attraction required in the

NN channel for the v2 8 model.

In future work it would be useful to fit the scattering data at

higher energies, including inelasticities. In particular the possible

existence of resonances in the S and P wave NA system, which would show up

in the 1D2 and 3F3 NN channels, could place significant constraints on the

nature of the diagonal NA-NA interaction. To make such fits, relativistic

effects and the instability of the A will have to be taken into account.

We hope to tackle this problem in the next year.

e. Consistency of Electromagnetic Current Operators andRelativistic Wave Functions (F. Coester and M. J. King*)

Intense electron and photon beams provide much of the precision

data on the structure of nuclei and the properties of nuclear matter.

Probing short range structure requires large momentum transfer which

inevitably involves relativistic effects. The directly observed quantities

are the matrix elements of the electric charge and current densities.

Inference from the data about the structure of the nuclear target requires

a mutually consistent representation of the current operators and the wave

functions representing the states of the target. The representations of

the Lorentz transformations depend on the forces governing the target

structure. It follows that current operators satisfying the covariance

relations of free particles are not covariant in the presence of

interactions. By combining results from quantum field theory and

constraint dynamics we have found a systematic construction of the two-body

current operators required by Lorentz covariance. The construction does

not depend on an expansion in powers of the particle velocities. A

preliminary report on this work was presented at the Sixth Pan American

Workshop on Condensed Matter Theory at St. Louis, Sept. 20-Oct. 1, 1982. A

paper for publication is in preparation.

*SOHIO Technical Center, Cleveland, Ohio.

137

f. Relativistic Quantum Mechanics of Particles with DirectInteractions (F. Coester and W. N. Polyzou*)

Relativistic quantum mechanics requires a unitary representation

of translations and Lorentz transformations on the Hilbert space of

states. Causality requires that systems localized in relatively space like

regions be dynamically independent at least for macroscopic distances. We

have realized both requirements by an explicit recursive construction for a

fixed arbitrary number of interaction particles. The Hamiltonian is in

many ways similar to the nonrelativistic many-body Hamiltonian. Under

conditions of physical interest the strength of the required N-body

interaction decreases rapidly with increasing N. The construction can be

generalized to allow for particle creation. Relativistic effects in nuclei

are the prime area of application of this theory. A paper on this work has

been published in Phys. Rev. D.

In its present form it is essential for theories of this type

that all particles and bound clusters become free when they are widely

separated, i.e., the forces are short range. The treatment of confining

forces involves new problems. Constituent quark models have been

quantitatively successful only for single hadrons. The construction

constituent quark models of multihadron systems is an open challenge. Work

on these problems is in progress.


g. Static Bag Source Meson Field Theory (John A. Parmentola)

An important factor in the role quarks will ultimately play in

nuclear physics is the size of the quark core of the nucleon. Is its

radius about equal to the charge radius of the proton or is it much

smaller? Chiral bags provide useful models for the study of the

consequences of various assumptions. The effective coupling to the meson

field is stronger for smaller bags. For "little bags" perturbative

treatment of the meson field or the truncation of the Fbck space to one or

two mesons do not yield legitimate approximations and some modes of the

meson field become collective degrees of freedom of the physical nucleon.

138

In general these collective degrees of freedom cannot be treated

classically. For exploratory purposes we have investigated in quantitative

detail a static source meson field theory in which only the nucleon isospin

degrees of freedom are coupled linearly to a scalar-isovector meson

field. We find that there exist reasonable values of the coupling constant

g (~4) and the source radius R (^0.3 fm) for which the strong coupling

approximation is valid. The lowest lying collective excitation of the

dressed nucleon is a rotational isospin mode with isospin i. If we allow

an intrinsic isobar excitation of the source (bare A) the strong coupling

approximation is valid for significantly smaller values of the coupling

constant or larger bag radii. In that case we find a bare A component in

the dressed nucleon of 36%. Meson nucleon scattering in this model has

been investigated numerically. A paper on this work has been submitted to

Phys. Rev. D. These results are encouraging. They justify the more

elaborate calculations required to treat the coupling of the pion field to

a little chiral bag with intrinsic excitations.

h. Monte Carlo Method for Chiral Bag Models (B. D. Day)

In chiral bag models of the nucleon, the meson field is coupled

to a static nucleon source with spin-isospin degrees of freedom. Various

approximation methods have been applied, and it is desirable to test their

accuracy. By putting the field on a spacetime lattice, the problem can be

formulated in terms of a path integral. Treating the path integral by the

Monte Carlo method would give reliable results to be compared with

approximate calculations. A possible problem is that the coupling to the

spin and isospin of the nucleon causes the integrand to be non-positive-

definite in the Monte Carlo calculation, which could spoil its numerical

accuracy. This has been tested in a preliminary study using a one-

dimensional lattice. Systems with as many as 40 lattice spacings were

treated. No loss of accuracy was found in the Monte Carlo method, which is

favorable for application to the full spacetime lattice. However, further

technical problems, such as subtracting the vacuum energy of the lattice

without loss of numerical accuracy, must be overcome before interesting

calculations are possible.

139

B. VARIATIONAL CALCULATIONS OF FINITE MANY-BODY SYSTEMS

S. C. Pieper, R. B. Wiringa, A. R. Bodmer, and collaboratorsfrom other institutions

Two approaches to calculation of finite many-body systems wereinitiated in 1983. One aim is to develop Monte-Carlo techniques forvariational calculation of the ground states of large finite systems ofparticles, with the ultimate aim of treating nuclei with realistic nucleon-nucleon potentials. The second problem under study is a modern treatmentof the binding of hypernuclei by including complex AN and ANNinteractions. Specific problems are discussed in the following.

a. Ground States of Quantal Many-Body Systems (S. C. Pieper,R. B. Wiringa, V. R. Pandharipande,* J. G. Zabolitzky,t andU. Helmbrecht )

In the past 30 years, there has been much progress in the

computation of the ground--state properties of infinite quantum liquids such

as nuclear matter or liquid 4 He or 3 He. For given interactions, accurate

calculations of the ground states of three- or four-particle systems have

also been made. However there has been relatively little work on quantum-

mechanical calculations of large (more than four particles), but finite,

systems of particles interacting with given potentials. We have begun to

develop Monte Carlo techniques for the computation of the ground state

properties of such systems. At Argonne and Urbana we are performing

variational calculations which give an upper bound for the ground-state

energy while Green's function Monte Carlo (GFMC) calculations are being

used at Bochum and Cologne. The latter method gives (up to statistical

errors) the exact ground-state energy and density distribution but requires

much lengthier calculations; these calculations are not possible on the

computers available at Argonne.

We have started by writing programs for droplets of liquid 4 He.

This is a simple system since we do not have to consider the complications

of spin degrees of freedom and antisymmetrization. Also the He-He

potential is a function of just the inter-atomic distance and the three-

body potential is weak enough to be ignored. The next case to consider is

*University of Illinois, Urbana, Illinois

tUniversity of Cologne, Cologne, Germany.

(Ruhr University, Bochum, Germany.

140

that of droplets of liquid 3 He. Here we will have to deal with spin and

antisymmetrization; however, the potential remains simple. Finally we hope

to be able to do useful calculations for nuclei using realistic (and hence

complicated) nucleon-nucleon potentials.

Although the liquid He droplet computations may be considered as

warm-up exercises for the calculation of nuclei, this work is interesting

in itself. The binding energies and radius parameters of the droplets may

be expanded as power series in N- 1 1 3 , where N is the number of atoms in a

droplet. The resulting series appear to be qualitatively different from

the results of the hydrodynamical approximations currently being used in

ne tron-star calculations. The extrapolation of such series to N= may be

compared with the infinite liquid calculations to learn something about the

reliability of the extrapolations used to find the "experimental"

properties of nuclear matter. It also appears that these series may give

the best available values for the surface energy of infinite liquids for a

given potential; there have been very few direct calculations of this

quantity.

b. Monte-Carlo Variational Calculations of 4He Droplets(S. C. Pieper, R. B. Wiringa and V. R. Pandharipande*)

A program for Monte-Carlo variational calculations of droplets

of 4He has been completed and is being used. In these calculations a

variational wave function containing one-, two-, and three-particle

correlations is used. The ground state energy is then a 3N-dimensional

integral, where N is the number of atoms in the droplet. The integral is

done by the Metropolis method. Because this is a variational calculation,

the parameters of the correlation functions must be varied until the

minimum ground state energy is found; this energy is then an upper bound on

the correct energy. We have already made calculations for 4 < N < 240 and

are planning calculations for N 700. The results for N < 100 can be

compared with the GFMC results and are found to le about 3.5% too high on

average.


141

0.02

Io .

IZI 0.0!

n

I I v I I I I II I I I I IIIUI I I I I I -Y

-N

40- 20

84 8112 240

3

4 8 12 16

728

J L I1 *l

20 24

Fig. 111-4. Density profiles of droplets of 4He as computed by GFMC(solid curves) and variational Monte Carlo (dashed curves). The

curves are labeled with the number of atoms in the droplet.

Most of the computer time for these variational calculations is

used in calculations of only moderate statistical accuracy in which the

parameters of the wave function are varied in an effort to locate the

minimum energy. Because our wave functions have 10 to 20 parameters, and

because the statistical errors in two Monte Carlo calculations can result

in an erroneous conclusion as to the best parameter set, this process can

be quite painstaking. To help alleviate this, we have derived integral

expressions for the first and second derivatives of the energy with respect

to the variational parameters. These integrals can be evaluated in the

random walk used to compute the energy and thus we can predict an improved

set of parameters (or recognize that we are at the best set) in about the

same time that it takes to evaluate the binding energy (see Fig. 111-4).

V l 1 l 1 7L 1 1 _

rI

142

c. S-shell Hypernuclei and A-nucleon Interactions (A. R. Bodmer,J. Carlson,* and Q. N. Usmani*)

We are making variational calculations of the binding energies of

the s-shell hypernuclei: H, AH and 4He, He. In contrast to earlier

calculations we include tensor 2-body and 3-body forces, and calculate the

energies of the excited J=1 states of AH and He. Furthermore we use

semiphenomenological 2-body AN and 3-body ANN interactions with shapes

based on two-pion and one-kaon exchange mechanism. The variational

calculations use the techniques and nuclear wave functions developed by the

Urbana group of V. R. Pandharipande and collaborators; in particular the

appropriate 2- and 3-body correlations are included.

So far our calculations have been mostly with central AN

potentials for AH and Ae. A distinctive feature of our approach is to

determine the effective 2-body AN (s-state) interactions from the 2-body

scattering data and from VH but not from the heavier hypernuclei for whic"

many-body-force effects may be important. Our preliminary results indicate

these AN potentials to be only slightly spin dependent, consistent with

earlier investigations, and to give a reasonable ground state energy

for AHe, again consistent with earlier results, but to give too small

excitation energies for the J=1 states. These preliminary results

thus indicate that the splitting between the ground and excited states of

the A=4 hypernuclei is due to 3-body ANN forces or some other many-body

modification of the AN interaction (such as suppression of the AN-EN

coupling as proposed by B. F. Gibson and D. R. Lehman). Our future

calculations should help to clarify this situation. We have also been

preparing for calculations of charge symmetry breaking effects in 4and 4He where there are problems of long standing involving the size of

Coulomb-nuclear interference effects and of the spin dependence of the AN

charge-symmetry breaking interaction. We have also been preparing for

calculations of 5He. A long standing problem has been the overbinding

of AHe with 2-body forces (such as ours) which fit the 2-body scattering

data and the ground state energies of AH and AH, AHe. The inclusion of the

tensor components in the AN and ANN forces as well as inclusion of

"dispersion" type ANN forces should help to clarify this problem.


14 3 //44

d. Alpha-Cluster Calculations of ABe and 'A Be (A. R. Bodmer,Q. N. Usmani,* and J. Carlson*)

We are making variational calculations of the hypernucleus ABe

and the double hypernucleus AABe assuming 2ac-A and 2c-2A cluster structures

for these hypernuclei, respectively. Earlier variational calculations

(including those of A. R. Bodmer and S. Ali) indicate that such cluster

models probably give a very good description of these hypernuclei. Such

cluster calculations then enable one to make quite reliable calculations of

the energies of these hypernuclei with fitted a-a and a-A potentials and

additionally some assumed AA potential for 10 Be. A reexamination of these

hypernuclei using such cluster models is timely because of improvements in

variational techniques of calculating few-body systems, in phenomenological

a-a potentials and also in the hypernuclear data. In particular 3Be is

currently perhaps the most reliably established AA hypernucleus, and its

analysis will therefore provide crucial knowledge of the AA interaction.

Also the binding energies of AHe and ABe are known more accurately than at

the time of the earlier calculations. Good calculations of Be are a

prerequisite for reliable calculations of AABe, as well as being of

interest in their own right. We have so far made variational calculations

of ABe for several available phenomenological c-a potentials and for a-A

potentials whose strengths are fitted to the binding energy of WHe and

whose shapes are obtained by folding effective AN potentials (obtained by

use of the Moszkowski--Scott separation method) into the c-particle density

distribution. It seems significant that we find ABe to be consistently

somewhat overbound (by about 0.5 MeV), consistent with the overbinding

of 5He and of a A in nuclear matter when central AN forces are used. We

are considering 3-body ANN dispersion type forces to see whether these will

account consistently for both the overbinding of 5He and Be. The

variational procedures for calculations of 0Be have been developed. We

shall use a two-pion exchange shape for the (singlet) AA potential, whose

strength will then be determined by the variational calculations for ABe

from the experimental value of the binding energy of 3Be.


145

C. NUCLEAR SHELL THEORY AND NUCLEAR STRUCTURE

D. Kurath, R. D. Lawson, and others

Our principal concern is to identify nuclear structure effects inthe results of current experiments. Interpretations were obtained for highspin states excited in heavy-ion reactions and for nuclear states prominentin inelastic scattering of pions, electrons,and protons. A major effort isbeing directed toward understanding the effect of including the A degree offreedom in structure calculations. The analysis of inelastic excitation bypions is also being extended by including effects of recoil.

a. High Spin States in 9 1 Tc (A. Amusa* and R. D. Lawson)

High spin states and their decay mode have recently been observed

in 9 1 Tc. In order to check the consistency of the tentative spin

assignments we have carried out a shell model calculation for this

nucleus. 3 8Sr50 was assumed to be a doubly closed shell core and the five

valence protons and two neutron holes in 23Tc48 were assumed to occupy the

2p1/2 and 1g9/2 single particle states. The residual two-body interaction

was taken from the work of Serduke, Gloeckner and Lawson. The shell-model

results support the experimental angular momentum assignments.

b. The 6 States in 2 8 Si (A. Amusa* and R. D. Lawson)d/ 2 + [d/ 2 7/2 6-

Experimentall, inelastic electron, pion and proton scattering to

the yrast (6~,l) state all indicate that the cross section should be

approximately 30% of the (d5/2)1 2 + (d5/2

1 1f7 /2) value, while the pion and

proton data to the yrast (6~,0) state yield an even smaller value, ~15%.

Stripping finds C2S = 0.24 and 0.19 for these T=O and T=1 states,

respectively, that is about 1/2 the pure configuration value. In addition,

the value of B(M1) between these two 6 states has been measured and is

(2.8 0.4)WN, where 1N is the nuclear magneton. This is only about 20% of

the (d 5 /2,f7/ 2 )-model value of 14.439 uN. We have carried out calculations

using the entire (d5/2 ,s1/2) model space for the 0+ ground state, and for

the 6 states the same (d 5 / 2 ,s 1 / 2 ) model space was used with at most one

nucleon allowed in f7/2. Two different (d5/2,s1/2) interactions that fit

the normal parity states near A = 28 were used and the ds-f 7 / 2 mat. .x

elements were calculated using the Schiffer-True potential. As shown in

Table IIP-Z a substantial decrease in the predicted cross sections and

146

transition rate are obtained. The calculations suggest that when some

aspects of the d3/2 level are included, theory and experiment may be

brought into agreement without the introduction of non-nucleoni degrees of

freedom. This work has been submitted for publication in Physical Review

Letters.

Table III-2. All 6 states in 28Si predicted to have eitherinelastic scattering strength, R, or spectroscopic strength, Q, greaterthan 5% of the pure (d5/2,f7/ 2) sum rule value. E is the predictedexcitation energy of the state and T its isospin. The value of B(Ml)connecting the yrast (6 1) and (6_,0) states is given. The calculationshave been carried out for two different (d5/2 ,s1/2) interactions.

WMHG Interaction Modified Surface Delta

E T R Q E T R Q

11.576 0 0.258 0.412 11.576 0 0.389 0.49512.818 0 0.135 0.190 11.918 0 0.065 0.07813.020 1 0.522 0.737 12.765 1 0.585 0.68914.108 0 0.101 0.162 13.952 0 0.084 0.04414.845 1 0.058 0.138 14.050 0 0.131 0.06715.143 0 0.136 0.120 14.571 1 0.037 0.05015.409 0 0.037 0.078 14.721 0 0.023 0.06816.327 1 0.053 0.019 15.153 0 0.043 0.06418.474 1 0.058 0.008 15.764 1 0.157 0.133

16.888 1 0.038 Q.056B(Ml; (6-,1) + (6-,0)) 6.47 PR8.32

c. Con ributiog of Giant Dipole State to Coulomb Excitationof Li and Li (F. C. Barker* and R. D. Lawson)

In Coulomb excitation of a nucleus, the direct E2 excitation of

the final states may be modified by interference with the two step process

involving virtual El excitation of high lying states in the giant dipole

region followed by El decay to the final state. To estimate this

contribution one must know the ratio of the matrix elements between the

initial and final states of the E2 operator compared to the square of the

El operator. To compute this ratio reliably it is not sufficient to

introduce an effective charge but instead one must consider configuration

mixing explicitly. We obtained magnitudes for the admixed states by

*Australian National University, Canberra, Australia.

147

projecting states of good angular momentum frn deformed Nilsson

orbitals. In this way we included excitations from the is to the (2s,ld)

shell and from the ip to the (2p,lf) levels. In first order perturbation

theory the amount of the mixing depends on a single parameter, AE, the

energy difference between the unperturbed and admixed states. QE was

chosen to fit the observed quadrupole moment of Li and with this choice

the predicted B(E2) values for 6Li and 7Li agree with experiment. Values

for the square of the El matrix element are being calculated.

d. The Effect of the A(1236) on the g-factor of Nucleons (R. D. Lawson)

The effect of including the A degree of freedom in the nucleus

has been examined. In first order perturbation theory we have shown that

the main effect on magnetic dipole properties of replacing a nucleon in the

nucleus by a A is to give a renormalization of the g factor of the valence

nucleons. In the meson exchange model the (NN)++(NA) transition potential

is the sun of a central spin dependent and a tensor interaction. We show

that the main effect of the central interaction can be taken into account

if one adds an effective operator 2gs T3 . For the tensor interaction

the main effect is an added operator g [a x Y2]1 yT 3. When the quark

model phasing between the central and tensor parts is used we show that

these two interactions contribute with opposite sign for magnetic moments

leading to a small change in u. For Ml transitions they come in with the

same sign and reduce B(M1) values by 20--30%. Numerical values for the g-

factors are given in Table 111-3. This work has been accepted for

publication in Physics Letters.

e. Beta Decay of 16C(O+) to 1 6N(0-) (D. Kurath)

In connection with a recent experimental measurement of this beta

decay, a shell-model calculation was carried out in the lowest order

(lp~1,2sd1 ) and (1p-2 ,2sd2 ) space. The calculated transition probability

is about (1/6) the value for a pure 2s1/2+lp1/2 transition, which is much

stronger than the observed value.

148

Table 111-3. Values of the g factors in nuclear magnetons fornuclei near the closed shells A16, 40, 90 and 208. The numberical resultsare for the transition potential of Smith and Pandharipande and thecontribution of the central and tensor parts are 1 s ed separately.Oscillator wave functions rere used (4-exp - 1/2cr ) with a= 0.598 fm~for the 0 shell, .563 fm for tie is and Od orbits, 0.497 fm- near A=40,0.453 fm at A90 and 0.3996 fm for Pb. If the quark model values areused in both the M1 transition operator and potential, the results must bemustiplied by 0.613. The effective M1 operator has

(Ml) = (3/40)1/2 {l(1) 3s(0) + T3 + g

+(n/2)1/ 2 (g(l) T3 + xg(0)[ 21y

P entral tensorA Orbit gs(g() (1) (0) (1 g(O)

is -0.244 0.0 0.0 0.0 0.0 0.0

16 Op -0.193 0.0 0.496 0.0 0.0 0.0

Od -0.175 0.0 0.471 0.0 0.0 0.0

is -0.302 0.0 0.0 0.0 0.0 0.0

ip -0.304 0.0 0.384 0.0 0.0 0.0

40 Od -0.265 0.0 0.368 0.0 0.0 0.0

Of -0.244 0.0 0.421 0.0 0.0 0.0

ip -0.418 -6.37 x10-4 0.323 -0.004 -0.002 7.47 x10- 4

90 Of -0.371 -1.13 x10-3 0.298 0.005 -0.004 1.33 x10-3

Og -0.331 -9.11x10-4 0.354 -0.005 -0.003 1.06 xlO-3

2s -0.525 0.0 0.0 0.0 0.0 0.0

2p -0.502 -2.93 x10-5 0.282 -0.026 -0.001 2.97xl0-5

ld -0.509 -2.53 x10-5 0.241 -0.018 -0.003 5.02 xl0-5

208 if -0.473 -4.14 x10-5 0.280 -0.028 -0.002 4.45 x10-5

ig -0.438 -9.35x10-6 0.292 -0.038 -0.001 2.47x10-6

Oh -419 1.70 x10-6 0.241 -0.027 -0.004 1.83 xl0-5

01 -0.372 -7.13 x10-5 0.279 -0.037 -0.003 8.27x10-5

14 9! b'

f. Analysis of Inelastic Scattering of Pions (T.-S. H. Lee andD. Kurath)

We have continued analyzing results from experiments of inelastic

scattering of '1 at pion energies near the (3,3) resonance, using a

combination of a DWIA reaction calculation with input results from shell

model calculations for particular states. The results for the 14N

experiment of the Argonne group have been published) and the 11B results

were presented at the Amsterdam conference and are in preparation for

publication. Our conclusion that a few J(LS) multipoles dominate the

strong transitions has been substantiated.

While the strong J-il transitions arise from the (LS)=(10)

multipole, the spin dependent (LS)=(ll) multipole is of interest because it

has a different angular distribution which peaks at 00, and its

contribution is largely incoherent with the (10) case. Recent forward

angle experiments at LAMPF are seeking such transitions, so a shell-model

survey of the (LS)=(1l) strength distribution has been done for 12C

and 1 4 N. There is a much broader distribution in energy than was true for

the (10) multipole.

1D. F. Geesaman et al., Phys.Rev. C 27, 1134 (1983).

151

D. INTERMEDIATE ENERGY PHYSICS

The intermediate energy pion-nucleus interaction is dominated bythe formation of the A resonance. The importance of the A degree offreedom in determining low energy nuclear properties and various nuclearreactions at higher energies has also received considerable attention inrecent years. Our study of intermediate energy physics has long been aimedat developing a unified many-body approach which can describe the A-nucleusdynamics both at low and intermediate energies. This is achieved byextending our conventional nuclear many-body theory to include the A and rdegrees of freedom. A separable model of such a many-body Hamiltonian wasconstructed by Betz and Lee in 1981 and has been applied in 1982 tosuccessfully understand various aspects of the A-nucleus dynamicsexhibited in pion-nucleus reactions. In 1983, the model has been extendedto account for the meson-exchange mechanisms. The constructed model fitsthe most recent NN scattering phase shifts in the entire energy region upto 1 GeV. The model can be used to explore whether the meson exchangemechanism can accurately describe the A-nucleus dynamics involved in pion-nucleus interactions and in high-energy electron nucleus scattering.

Our DWIA model for pion scattering has been extended to includenucleon recoil effects and also to account for the possible effects due tothe A component in nuclear wave functions. This improved DWIA model willbe used in 1983-84 to further explore nuclear structure in pion inelasticand charge-exchange scattering.

In 1982, we also investigated high energy electron scatterngfrom nuclei. The cross section of producing hypernuclei by the (e,e'K )reaction is predicted to be achievable by the proposed few GeV electronaccelerator. Work has also been done to investigate the A excitation inelectron scattering from light nuclei.

a. Phenomenological Many-Body Hamiltonian for Pions, Nucleons,and A Isobars (T.-S. H. Lee)

To study both the intermediate energy pion nucleus interaction

and the A degrees of freedom in nuclei, we have constructed a many-body

Hamiltonian for pions, nucleons and A isobars. The basic mechanisms of the

model consist of: (a) a two-body interaction VO between all two-baryon

states NIT, NA and AA, (b) a wN A vertex interaction in the resonant IN(3,3) channel, and (c) a two-body interaction V N in other iN channels.The interactions are determined by fitting the IN phase shifts up to 300

MeV and NN phase-shifts up to 1 GeV. A separable model of such a

Hamiltonian has been used to study various aspects of the A-nucleus

dyruwics (see Sec. D.b. and D.c.). If the interaction VO is not separable,

such as that derived from the meson-exchange mechanism, the correct

treatment of NN three-body branch cut at E > 300 MeV comprises the major

152

numerical problem in practice. In 1983, we have successfully developed a

practical numerical method to overcome this difficulty. The method has

been applied to explore the consequences of various meson-exchange models

in describing NN scattering up to 1 GeV. The major results are: (a) the

dynamical effects due to the vertex interaction N A and the NN interaction

in the NN channel are important at E > 400 MeV and (b) the meson-exchange

model of the Paris potential can describe reasonably well the most recent

NN phase shifts up to 1 GeV. A paper describing the method and the results

has been submitted for publication in Physical Review Letters. The

calculated p-p phase-shifts are compared with the Arndt's phase shifts in

Figs. 111-5 and 111-6. Our goal in 1983-84 is to explore the consequences

of the meson-exchange model in describing NN polarization cross sections,

and to investigate the problem of dibaryon resonance by also considering

short-range quark-gluon dynamics.

b. A Microscopic Study of A-Nucleus Dynamics (T.-S. H. Leeand K. Ohta*)

In the one-hole line approximation, the self energy of A

propagation in nuclear matter is calculated from the separable model

Hamiltonian for Tr, N and A constructed by Betz and Lee. In the local

density approximation, the calculated A self energy corresponds to the

strength of the A-nucleus potential which is determined phenomenologically

in the A-hole doorway model of pion-nucleus scattering. We find that our

calculated strength of the central potential is on the average about 80% of

the empirical one. However, the calculated spin-orbit potential is much

smaller than that of the A-hole model. We also find that pion absorption

through the NA S wave only accounts for about half of the total

absorption. The sum of the other partial waves is found to be equally

important. A paper describing our study has been published in Phys. Rev. C

25, 304 (1982). In 1983-84, we plan to reinvestigate this problem with the

newly constructed meson-exchange model Hamiltonian described above.


153

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so o0oo0o0~0

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0

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Fig. III-5. The calculated pp scattering phase shifts up to 1000 MeV

are compared with Arndt's phase shifts.

C

-40

20-

201

1000 N0OE(MeV)

- -

-

P-..

8s

'I

3

0

154

500

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- -0

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Fig. 111-6. The calculated pp scattering phase shifts up to 1000 MeVare compared with Arndt's phase shifts.

U)

a)a)

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155

c. Absorption of Pions by the A=3 Nuclei (T.-S. H. Lee andK. Ohta*)

Within the separable model Hamiltonian of Betz and Lee, we have

studied the absorption of pions by 3He. Keeping only the intermediate

states involving at most one pion or one A and neglecting two nucleon

interactions in the TrNNN channel, we express the absorption amplitudes in

terms of a three-body amplitude defined in the coupled NNNONNA subspace.

The resulting three-body equation has been solved by using the iteration

method due to Kloet and Tjon.

Our first important result is that the strong isospin dependence

observed in pion absorption on 3He can be described by tite two-body

mechanism wNN - AN - NN. Our results for 165-MeV pion energy is shown in

Fig. 111-7. The effect of the three-body mechanism is also calculated but

found to be negligibly small. The AN - NN dynamics consistently determined

from NN inelasticities is shown to be essential to understand the isospin

dependence. A paper describing this result has been published in Phys.

Rev. Lett. 49, 1073 (1982). Our prediction of the angular correlation of

the 3He(ir+,pp) reaction at 75 MeV has been confirmed by a recent

measurement at TRIUMF. In 1983-84, we plan to complete the analysis of

this new data as well as the data to be obtained at LAMPF. Our objective

is to explore the extent to which the pion absorption by nuclei can be

described by the two-body mechanism WNN-NA-NN.

d. Electroproduction of A From Light Nuclei (T.-S. H. Lee andK. Ohta*)

The dominant mechanism in (e,e') on nuclei when the energy

transferred to the nucleus is about 300 MeV involves excitation of a

nucleon to the A state. The kinematic conditions of A creation by the

virtual photon are quite different from those in the pion-nucleus

interaction. Since the virtual y interacts weakly with the nuclear medium,

the A can be produced throughout the nuclear volume, whereas the pion

produces A's mainly on the nuclear surface. Furthermore if the incident

electron energy is several GeV, one can produce very fast off-shell A's

with momenta of many GeV/c. The A produced in the n-nucleus interaction is


156

'-n 1000- -

} 010 0 (7r,+ p p )

10P

10-

b 0~ 0.0 j(r-,pn)

440 480 520 560 600p1 (MeV/c)

Fig. I1I-7. Momentum spectra of He(r ,pp) and He(7r,np) at 01 = 550and 02 = 1000 are compared with the data of ANL [Phys. Rev. Lett.47, 895 (1981)].

157

mainly on-shell with momentum about 0.3 GeV/c. Therefore the (e,e') study

can examine the dependence of A-nucleus dynamics on the nuclear density and

on the A momentum. We are studying the electroproduction of A from the

deuteron and 3He by adding the vertex interactions yN-A and YN«N to our

many-body Hamiltonian for IT, N and A (described in Sec. IV.A.a.). Partial

wave analysis needed for carrying out the calculations of d(e,e') has been

completed. A computer program for numerical calculation is being

developed. The calculations for 3He are closely related to our study of

pion absorption by 3He (Sec. D.c.) and can be carried out by using the same

numerical method. We expect to obtain results in 1983-84. Our objective

is to explore the usefulness of the proposed few GeV electron accelerator

in the study of A-nucleus dynamics.

e. A Nonstatic DWIA Model for Pion Scattering (T.-S. H. Lee)

Our DWIA code has been widely used by many groups to interpret

pion-nucleus inelastic scattering data. The program has now been extended

to include nucleon recoil effects in the rN t matrix. This improvement of

the DWIA model is needed to account for the contribution from the

transverse nuclear form factors which dominate some nuclear excitations due

to pions. The model has also been extended to account for the possible

effect of the A component in nuclear bound state wave functions, assuming

that the IN + A transition can be related to the irN + IN interaction in

the quark model. In 1983-84, we will use this improved DWIA program to

further explore nuclear structure effects in pion inelastic and charge-

exchange scattering.

f. Production of Hypernuclei by Few GeV Electrons (T.-S. H. Leeand J. P. Schiffer)

In the one-photon-exchange approximation, we have estimated the

cross section of the production of hypernuclei by (e,e'K+) reactions. The

angular correlations and energy dependences of 12C(e,e'K+) reaction have

been calculated for various kinematics of coincidence measurements. It is

shown that a few GeV electron accelerator is very efficient for carrying

out such a study. In Fig. 111-8 we show the calculated cross sections with

2-GeV electrons. The results are included in the ANL proposal of GEM to

the Department of Energy.

158

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The upper figure shows angular correlations for fixed inelastic energyand various electron angles (the kaon angle is on the side opposite tothe electron). The lower figure shows the electron spectrum for fixedgeometry.

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g. A Model of Elastic and Inclusive P-Nucleus Scattering Above 500 MeV(J. A. Parmentola and H. Feshbach*)

In the impulse and closure approximations, we have developed a

coupled-channel model of p-nucleus scattering based upon the KMT expansion

of the optical potential to second order in the 2-body scattering

matrices. In this model, the inelastic channels are represented by a set

of effective channels. The essential idea of the method is to choose the

effective channel basis such that the infinite number of physical channels

can be approximated by a finite number of effective channels. In the

closure approximation, the inclusive cross section is obtained by summing

over all physical channels, however the effective channel basis provides an

equivalent and economical evaluation of this quantity.

We have applied this model to P- 4 He scattering at 1 GeV and we

have compared our results for elastic scattering to the method of

calculation of Feshbach, Gal, and Hiifner with the same input data. The

advantage of our method is that it is economical and numerically exact,

while the FGH method is approximate and difficult to improve. The

comparison of the two methods reveals significant discrepancies. We are

currently trying to track down the origin of these discrepancies.

*Massachusetts Institute of Technology, Cambridge, Massachusetts

161

E. HEAVY-ION INTERACTIONS

S. C. Pieper, M. J. Rhoades-Brown,*, A. R. Bodmer, and others

Our theoretical effort in heavy-ion interactions has been

concerned with two kinematically different regions. One is concerned with

low energies, up to several times the Coulomb barrier. Here we havedeveloped a large program, Ptolemy, for the coupled-channels computation ofinelastic scattering. This program is now essentially complete, and is inuse by both theorists and experimentalists at a number of locations inaddition to Argonne. Two current examples of such calculations are givenbelow.

The second kinematic region deals with collisions at energiesabove about 100 MeV/nucleon where one may encounter conditions of highdensity and temperature at which new states of nuclear matter may exist.We initiated and are continuing classical-equations-of-motion (CEOM)calculations of high-energy heavy-ion collisions. The CEOM method is acompletely microscopic but classical approach whose essence is thecalculation of all nucleon trajectories using a two-body potential between

all pairs of nucleons. The unique feature of this approach is that itincludes finite-range interaction effects (in particular potential energyeffects) and hence does not assume that nuclear matter is a dilate gas asdo cascade calculations. On the other hand, in contrast to hydrodynamics,the CEOM approach is a microscopic one and does not assume localthermodynamic equilibrium.

*Oak Ridge ' tional Laboratory, Oak Ridge, Tennessee.

a. Analysis of 2 8Si+2 8Si Scattering (S. C. Pieper andM. J. Rhoades-Brown*)

Within the last few years, extensive data on the elastic and

inelastic scattering of 28Si from 28Si have been measured at Argonne and

Brookhaven. Inelastic channels up to the mutual excitation of the 4+ and

6+ states are resolved; in the vicinity of 900, channels such as the mutual

4+ ,4+ contain most of the cross section. We have attempted to analyze this

data with large coupled channels calculations. Because of the strong

deformation of 2 8 i 2 ~~ -0.4) we find it necessary to include A = 0, 2, 4

and 6 projections for both the projectile and target of the deformed

potential. Our biggest calculations contain 169 coupled equations with

almost 25,000 coupling- terms. We find that with reasonable potentials we

can reproduce either of the two qualitative features of the data: (1) the

smooth decay of the elastic differential cross section out to about 700 or

*Oak Ridge National Laboratory, Oak Ridge, Tennessee.

162

(2) the very strong excitation of the high-lying mutual excitation channels

at 90*. However we have not found one potential that predicts the

qualitative features of the data over the entire angular region. Work on

this problem is continuing.

b. Analysis of 160 and 180 Scattering from 54Fe (S. C. Pieper andS. Landowne*)

With an 160 projectile, the backwards excitation function for the

first 2+ state of 5 4Fe shows a pronounced Coulomb-nucleon interference

minimum. However this minimum is filled in when 180 is used as the

projectile. We attempted to analyze this difference by first using the

160+54 Fedata to determine optical parameters for the 1 6 0+5 4 Fe system.

The resulting potential was then used as a core potential for the

1 80+54Fe system with the effect of the two additional neutrons in 180 being

accounted for by a n+5 4 Fe optical potential. These potentials were used in

coupled-channels calculations that, for the 180 projectile, included

excitation of the 2+ states of 180 and 54Fe and mutual excitation. Good

fits were obtained to both the elastic and inelastic 160 data, but the

resulting 180 potentials did not accurately predict the 180 elastic cross

sections, nor did they predict the filled in minimum of the inelastic

scattering. Work on this problem will be continued in Munich this summer.

*University of Munich, Munich, W. Germany.

c. Extension of the CEOM Calculations (A. R. Bodmer and C. N. Panos*)

We have been developing the CEOM calculations to allow for Pauli

blocking effects in the one-body phase space. This is being done by

incorporation of probabilistic elements in the scattering using appropriate

binning of the phase space. Developments so far look encouraging but will

require more efficient or faster calculations of the many-body

trajectories. Inclusion of Pauli blocking effects would make the CEOM

approach more applicable to higher densities and especially to lower

*University of Ioannina, Ioannina, Greece.

163//16+

energies, namely in the range of about 50--200 MeV/nucleon where there is

currently no suitable microscopic description. We have also been

considering momentum dependent 2-body potentials together with other

procedures in order to obtain more satisfactory binding and nucleon-nucleon

scattering properties, in order to allow study of a larger range of

projectile and target nuclei, and also more realistic equations of state.

165/4(L;

F. OTHER THEORETICAL PHYSICS

a. Angular Momentum Near Solenoids and Monopoles (Murray Peshkinand Harry J. Lipkin)

Interest in some of the quantum mechanical consequences of

electromagnetic angular momentum has recently been renewed by two unrelated

developments. Firstly, it has been appreciated that the quantum mechanical

constraints on the scattering of an electron by a magnetic monopole at

near-zero impact parameter have important implications for the nature and

mass scale of the monopole. Secondly, there has been an interesting

suggestion that a composite made of an electron and an infinitely long

solenoid may have unusual statistics because it can have nonintegral

orbital angular momentum. We have examined the nature and location of the

electromagnetic angular momentum which arises from the Poynting vector

produced by crossing the electric field of the electron with the external

magnetic field. We show that proper inclusion of the solenoid's return

flux removes the nonintegral orbital angular momentum, and that neglect of

the return flux by making it disappear at infinity leads to unphysical

results. We also show that the origin (in the relative coordinate) must be

excluded for kinematical reasons due to angular momentum quantization when

an electron is scattered by a fixed monopole. This work has been published

in Physics Letters 118B, 385 (1982).

b. Triplet Correlations in Spin-Aligned Deuterium (Robert M. Panoff)

The question of the stability of spin-aligned deuterium was

investigated using a wave function which incorporated the possibility of

three-particle correlations. An improved variational Monte-Carlo code was

used, and at low density it was found, as expected, that very little

additional binding (0.01 K) resulted from the added correlations. The code

was expanded to allow the calculation of the resultant one-body density

matrix.

IV. THE SUPERCONDUCTING LINAC

R. Benaroya, J. M. Bogaty, L. M. Bollinger, R. C. Pardo,

K. W. Shepard, G. P. Zinkann, J. Aron,* B. E. Clifft,*

K. W. Johnson,* P. Markovich,* and J. M. Nixon

INTRODUCTION

The activities concerned with advancing the technology of thesuperconducting heavy-ion linac now have three major components. One isthe specific task of completing and refining the prototype superconductinglinac that functions as an energy booster for heavy ions from the tandemelectrostatic accelerator. The second part consists of continuinginvestigations of various aspects of superconducting rf technology, some ofwhich are of fairly general interest for accelerator technology. The thirdundertaking is the line-item project to extend the present tandem-linacaccelerator into a substantially larger system called ATLAS.

All parts of the superconducting linac program are jointlysupported by the Chemistry and Physics Division.


169/)'70

A. PROTOTYPE HEAVY-ION SUPERCONDUCTING LINAC

This project, started in mid-1975 and now completed, has beenconcerned with the design, construction, installation, and testing of asmall superconducting linear accelerator (linac) to serve as an energybooster for heavy-ion beams from the FN tandem accelerator. The principalobjectives of the project have been to develop a new accelerator technologyand to build the prototype for a heavy-ion energy booster that can be usedto upgrade the performance of any tandem accelerator. The overall designis highly modular in character in order to provide maximum flexibility forfuture modifications and/or improvements. The last two resonators of theplanned 24-resonator system were installed in 1982.

The booster linac is now complete in all respects. Its mainfeatures have been outlined in previous Annual Reviews. Some effort isstill being devoted to perfecting various subsystems of the accelerator, asoutlined in Sec. V, and this effort is resulting in a machine of excellentreliability. However, our developmental effort is now being devoted mainlyto the ATLAS project.

By now, the booster has been used extensively ('10,000 hr) toprovide beams for nuclear-physics research. This operational experience issummarized in Sec. V of this document.

The booster will continue to be used in its present form untillate 1984 or early 1985, when it will be incorporated into the ATLASfacility.

171

B. INVESTIGATIONS OF SUPERCONDUCTING-LINAC TECHNOLOGY

This program includes several investigations of applications ofsuperconducting technology to the acceleration of heavy ions. At thepresent time, the choice of work is guided principally by the urgentdevelopmental needs of the heavy-ion booster and especially for ATLAS.Most of this work is included within the following topics: (a)superconducting accelerating structures, including studies of the phenomena

that limit performance, (b) time-of-flight technology for pulsed beams,and (c) superconducting magnets for heavy-ion beams.

1. Superconducting Accelerating Structures

K. W. Shepard, G. P. Zinkann, and P. Markovich*

The development of superconducting accelerating structures forheavy-ion acceleration is proceeding on a broad front. This work includes(1) the development of the new class of resonator for use in ATLAS, (2)efforts to improve the performance of the two existing classes ofresonators, and (3) the development of a new slow-tuner controller.

a. The ATLAS Resonator

For ATLAS it is desirable to have a resonator that is optimum for

an ion velocity that is substantially higher than the present S = 0.105

unit. After a thorough design study, it was concluded that the best choice

for our needs would be a split-ring resonator operating at 147.5 MHz (3/2

times the present frequency) in the same housing as the present 0 = 0.105

unit. This choice maximizes the acceleration of ions with S = 0.16. By

optimizing the shape of all parts of the drift-tube assembly, it is

expected that the accelerating field will be increased. This type of

resonator and its older brothers are pictured in Fig. IV-1.

As was reported last year, a first prototype resonator was

completed and partially tested in early 1982. Further tests showed that

the unit had a good Q at low fields, but the maximum achievable

accelerating field was limited to about 2 MV/m, less than half of the

expected value. Although the test results were inconclusive, the data

strongly suggested that at least two of the welds in the structure were

defective. However, efforts to repair the welds were unsuccessful.


jll

Fig. IV-l. The three classes of resonators to be used in ATLAS. On the left and right, respectively,

are the proven S= 0.105 and S = 0.060 units that operate at 97 MHz. The new ATLAS unit, designed

for 6= 0.16 and 145.5 MHz, is in the middle. All three units have housings with an inside diameter

of 16 inches.

11

f

1

s

1'

173

In view of the problems with the first prototype resonator, the

fabrication of a second prototype was started in June 1982. Considerable

effort was devoted to control of the quality of the welding process and to

an x-ray examination of each weld. This effort delayed the fabrication

schedule but has at least resulted in welds that appear to be of superior

quality.

The second prototype resonator was completed in January 1983, and

testing started immediately. The low-field Q of the unit is found to be

high. Also, it can be operated stably at an accelerating field well above

4 MV/m, thus indicating that the welding problem experienced with the first

unit has been solved. However, a drop in Q that appears to result from

electron loading sets in at a relatively low field, and consequently the

useful accelerating field is only about 3.3 MV/m, about 30% lower than was

expected. The cause for this problem has not yet been identified.

Intensive work on the resonator is continuing.

b. Resonator Accelerating Field

During the past year the last resonators for the prototype linac

were completed and installed. Most of our recent resonators are of

excellent quality, but two of the low-S units have exceptional

performance. The best of these was operated at an accelerating field of 6

MV/m with a power loss of only 4 W and was operated stably at 8 MV/m. This

latter value of the accelerating field corresponds to a maximum surface

electric field of 39 MV/m, probably a record high value for this

quantity. The reason for the outstanding performance of the resonator is

not known, but the result is nevertheless judged to be important because it

proves that it is feasible to improve considerably the performance of our

other resonators.

c. Restoration of Performance

During the past year, some of the resonators in the prototype

linac had been in continuous use for more than three years, and the Q of

some units had degraded so much that they were not useful. Previously, we

174

had demonstrated that such units could be restored to their original

performance by disassembly and electro-polishing, but this procedure is not

entirely satisfactory because it is relatively time consuming.

Consequently, we have tried the much simpler procedure of ultra-sonic

cleaning and rinsing the surfaces with water and several organic

solvents. It was found that this technique restores the performance of the

unit almost completely, both with respect to Q and maximum accelerating

field. This result is interesting not only because it establishes a simple

method for restoring the performance of long-used resonators but also

because it shows that the resonators do not suffer any fundamental

degradation in some 10,000 hours of operation.

d. Slow-Tuner Controller

(K. W. Johnson,* B. E. Clifft, and K. W. Shepard)

After several unsuccessful attempts, a new type of slow-tuner

pressure controller that meets all requirements has been developed and

thoroughly tested. It is now in use on all of the resonators of the

prototype linac and will be used in ATLAS. There have been no failures of

the new system during the six months that it has been in use on the

prototype linac.

2. Time-of-Flight Technology

R. C. Pardo, K. W. Johnson,* and B. E. Clifft*

The effort to develop time-of-flight technology as a major tool

in the control and use of the prototype linac has continued. The main work

during the last year has been the continuing effort to refine the energy-

measurement system that makes use of the phase difference between two beam-

excited resonators.

The validity of the concept involved in our energy-measurement

system was demonstrated several years ago. However, it turned out that its

electronic system was not able to respond properly to the confusion that


175

results when a resonator in the linac goes momentarily out of lock, and

consequently the energy-measurement system has not been much used. Now the

electronic problems have been eliminated, however, and the beam energy can

routinely be measured continuously and non-destructively with an accuracy

of about two parts in 104. Unfortunately, this capability is available now

only on the +190 beam line, which feeds the 60-in scattering chamber and

the magnetic spectrograph. In time, the capability will be extended to the

other beam lines.

3. Superconducting Magnets

a. Prototype Bending Magnet

Work on the prototype superconducting magnet has proceeded

vigorously during the past year. The coil has been rewound, the cryostat

fabricated, machining of the iron completed, and the system assembled.

Testing is expected to start in April 1983.

Although the magnet being developed is viewed as the prototype

for several possible applications, it has design characteristics that are

well matched to what is required of a beam-switching magnet in the ATLAS

experimental area, and the prototype itself may end up in this application.

b. Heavy-Ion Beam Splitting

In the ATLAS system, we expect to split the beam into two

components in the interface region between the present and the future linac

sections. Two different kinds of magnets are being studied for this

application: (1) a superconducting septum magnet and (2) a hybrid system

consisting of an iron magnet with a field-free region produced by a

superconducting super-tube. Both approaches appear to be attractive

solutions to a difficult technical problem but both also involve some risk,

since neither approach has been tried previously.

176

4. Near-Term Plans

Much of the effort in 1983 and 1984 will continue to be devoted

to problems that are closely related to the refinement of the present linac

and especially to the needs of ATLAS.

If necessary, work on the a = 0.16 resonator for ATLAS will be

given a high priority. At this time, it is too early to know exactly what

questions will be addressed, but if the experience with this new design is

similar to that with earlier resonators, there will surely be some problems

that need to be studied.

A related area that requires further work is the investigation of

the factors that limit the performance of resonators. Now that we have

three classes of resonators with somewhat different parameters, we expect

to see performance patterns that will suggest models to be explored.

A considerable effort will be devoted to superconducting magnets

during 1983 and 1984. In particular, the work will focus on the special

magnets to be used for beam separation in the 40*-bend region of ATLAS.

Since this area of work is little explored, it is likely to lead to new

paths that are as yet unforeseen.

By late 1985, the ATLAS linac will be assembled and a sizable

effort will need to be devoted to studying its characteristics. In

particular, matching the beam from the present linac into the ATLAS linac

may be time consuming initially and may require the development of new

diagnostic techniques. In any case, the characteristics of the new kind of

beam splitter will be thoroughly studied.

C. THE ATLAS PROJECT

The Argonne Tandem-Linac Accelerator System (ATLAS) is a heavy-

ion accelerator being formed by enlarging the booster linac and by adding a

large new target area, as shown in Fig. VI-2. The resulting system,

consisting of the existing tandem and a 7-section linac, will have a

performance that is approximately equivalent to that of a 50-MV tandem with

two strippers.

4FN TANDEM

TARGET AREA I

( F

ATLAS - -TARGET

T RUCK -A-R- A

E NT RANCE ---- --

ION SOURCEOUTUT -- - -

SYSTEM BEAM LINE- -: -. - --

REBUNCHER

BEAMDIAGNOSTICS

TERMINAL -a-!- - - - ~ -

ADD\TION

H A TARGET

AREABOOSTER LINACLII

ACCELERATOR 40*O1 03 05CONTROL BEND 010 20 30 40 5

ROOM SCALE (feet)

Fig. IV-2. Layout of the ATLAS facility. The building areas shown in grey (dotted) and the

accelerator components shown fully darkened are being added by the ATLAS project.

178

ATLAS is aimed squarely at the needs of precision nuclear-

structure physics, providing beam energies up to 25 MeV/A, easy energy

variability, and beams of exceptionally good quality. The short-pulse

character of the beam will be emphasized so as to maximize its usefulness

for time-of-flight and other timing measurements. An unusual feature of

the facility is the capability of providing beams simultaneously for two

independent experiments without a loss of intensity to either.

The ATLAS project was authorized in the FY 1982 budget at a level

of $7.7 million, of which $4.0 million was appropriated in FY 1982, and the

remainder in FY 1983. The project started officially in January 1982 when

the initial funds were released. By the end of this reporting period

(March 1983), the project was about 40% completed.

The construction of the ATLAS building addition got off to a very

fast start and, because of economic conditions in the building industry,

this has probably resulted in a considerable savings in cost. The first

phase of construction, consisting of foundations and poured-concrete walls,

was started in May 1982 and completed in October. The remaining work

started in December 1982, and by the end of the present reporting period

the building superstructure is in place, the enclosure of the building is

nearing completion, and work on building services has started. We expect

to start occupying the new building before Christmas 1983.

One of the main technical objectives of the ATLAS project is to

add three linac sections that can effectively accelerate the relatively

fast projectiles produced by the booster linac. This required the

fabrication of 18 new resonators. Our present plan is to have the first 6

of these be of our proven S = 0.105 type in order to make it easy to match

the beam from the booster into the new linac. The other 12 units will be

of a new type that is optimum for ions with S = 0.16 and operates at an RF

frequency of 145.5 MHz, 3/2 times the frequency of the booster units. The

status of development of the new accelerating structure is summarized in

section VI.B.l.a.

Because the accelerator addition involved in ATLAS is closely

similar to the existing prototype linac, it was possible to start the work

on major components as soon as funds were released. Consequently, rapid

progress has been made. Cryostat fabrication is now largely completed, and

179// 0

one unit is expected to be ready for operation with installed resonators by

late 1983.

Unlike the booster linac, we plan to start operation of the full

ATLAS system only when all resonators are in place. Officially, this major

milestone is scheduled for April 1985, but obviously we are trying to beat

this schedule. In the meantime, the 24-resonator booster linac will

continue to be intensively used for research in the present experimental

area.

1811f/ 5$'

V. ACCELERATOR OPERATIONS

Introduction

This section is concerned with the operation of both the tandem-linac heavy-ion accelerator and the Dynamitron, two accelerators that areused for entirely different research. Developmental activities associatedwith the tandem and the Dynamitron are also treated here, but developmentalactivities associated with the superconducting linac are covered separatelyin Sec. IV, because this work is a program of technology development in itsown right.

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A. OPERATION OF THE TANDEM-LINAC ACCELERATOR

The tandem-linac accelerator is operated as a source of energetic

heavy-ion projectiles for research in several areas of nuclear physics and

occasionally in other areas of science. The accelerator system consists of

a 9-MV tandem electrostatic accelerator and a superconducting-linac energy

booster that can provide an additional 20 MV of acceleration. Figure V-1shows the layout of this system, which will be operated in its present form

until the end of 1984, when it will be incorporated into the larger ATLASsystem. In both the present and future forms the accelerator is designed

to provide the exceptional beam quality and overall versatility requiredfor precision nuclear-structure research.

Some aspects of the technology of the superconducting linac are

discussed in Sec. IV.

1. Operation of the Accelerator

The tandem-linac has been operated routinely and effectivelyduring much of the past year as a research tool, mainly but not exclusively

for nuclear physics. Some statistics about the operation are summarized in

Table V-I, and representative beams that have been accelerated during the

past year are described by Table V-II.

A notable feature of the use of beams from the accelerator is theincreasing involvement of outside users, as indicated by the data of TableV-I. In particular, the running time allocated to outside users is

expected to increase from 35% in FY 1982 to 51% in FY 1983.

The overall quality of the operation has improved greatly duringthe past year, partly because of the technical improvements summarizedlater and also because of a change in the way in which the linac isoperated. In the first few years of operation, the beam user was

responsible for the operation during all but the day-time shifts. Thisarrangement was necessary in order to minimize costs, but it was

undesirable because it resulted in reduced running efficiency. The problemwas largely eliminated in May 1982 when qualified operator/engineers werescheduled to be present during the evening shifts. This added manpoweralso made it possible to expand the running schedule from five to six

twenty-four days per week, i.e., from Monday morning to Sunday morning.

Because of funding limitations in FY 1983, it has recently(February 1983) been necessary to reduce the running schedule back to afive-day week. Moreover, the accelerator will be shut down for at leastsix weeks in order to reduce operating costs. Since these reductions arein addition to the down times required for various accelerator-improvementactivities (including ATLAS), the total running time in FY 1983 is expectedto be considerably less than in FY 1982. This reduction is especiallypainful at this time because there is now an intense demand for runningtime and the superconducting linac is now an excellent research tool.

It is believed that it will be feasible to return to a six-dayper week operating schedule in FY 1984.

TARGET AREA I

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Layout of the present tandem-linac facility. The experimental apparatus shown on the figure

is now all functional.Fig. V-1.

I

)i

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Table V-I. Operation of the ANL tandem-linac heavy-ion accelerator.

Fiscal Year

1982 1983*

Distribution of Machine Time (hr)

Research

Tandem-Linac System 3,077 2,350

Tandem (stand alone) 437 180

Tuning 497 190

Machine Studies 397 600

Unscheduled Maintenance 714 450

Scheduled Shutdown 3,640 4,990

Total (1 yr) 8,760 8,760

Distribution of Research Time (%)

ANL Staff 65 49

Universities (U.S.A.) 26 40

DOE National Laboratories 2 2

Other Institutions 7 9

Total 100 100

Outside Institutions Represented

Universities (U.S.A.) 12 13

DOE National Laboratories 1 3

Other 7 8

Data derived from experience to May 1983 and projection thereafter.

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Table V-II. Representative beams accelerated by the ANL tandem-linacduring the period 1 April 1982-31 March 1983. The quantities q1 and q2 are'the ion charge states after the terminal stripper and the post-tandemstripper, respectively.

Particle q1 q2 Tandem Energy Linac Energy(MeV) (MeV)

12C 5 5 51.0 107160 6 8 59.5 171170 6 8 59.5 15219F 7 9 68.0 1962 4 Mg 7 10 68.0 21228Si 8 13 76.5 2653 0 si 7 12 68.0 21432S 9 14 85.0 242

34S 8 13 76.5 2663 5C1 8 13 76.5 1973 7C1 9 14 85.0 268

40Ca 9 14 85.0 2524 8Ti 9 15 85.0 3245 8Ni 10 19 93.5 41060 Ni 10 19 93.5 32764 Ni 10 19 93.5 38982Se 11 20 102.0 308

2. Status of the Superconducting Linac

The last two resonators of the prototype superconducting linacwere installed and put into operation in October 1982, thus completing the24-resonator system. When these resonators are operated at their maximumlevels, the accelerating power of the combined tandem-linac system isroughly equivalent to that of a 24-MV tandem with two strippers forprojectiles in the range 25 < A < 70.

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3. Linac Improvements

(J. Aron, R. Benaroya, J. Bogaty, L.M. Bollinger, B. E. Clifft,K. W. Johnson, P. Markovich, J. M. Nixon, R. C. Pardo, and K. W. Shepard)

The pace of development of the prototype linac continues to slow

down as the various problems are solved and the emphasis is shifted to the

ATLAS project. Nevertheless, significant improvements continue to be made.

a. Resonators

The final two resonators of the booster were completed and

installed in the linac in October 1982.

b. Slow-Tuner Pressure Control

A slow-tuner pressure controller that satisfies all requirements

has been developed and installed on all resonators. The excellent

performance of this new system has eliminated one of the main operational

problems of the linac.

c. Liquid-Nitrogen Distribution

A new liquid-nitrogen distribution system with vacuum-insulated

lines and other refinements was installed in March 1982. Since then, there

have been no failures of the LN system, which had previously been a

frequent source of trouble and lost running time on the linac.

d. Helium Compressor

The third compressor for the model 2800 helium refrigerator has

been installed. This compressor will be needed to cool the ATLAS linac.

e. Energy-Measurement System

The beam-energy measurement system that makes use of two beam-

excited resonators has been considerably refined during the past year and

is now used frequently to monitor the beam energy. Numerous electronic

problems have been eliminated and the system can routinely and non-

destructively measure the energy with an accuracy of a few parts in 10.

The new system is now expected to be the primary source of information

about beam energy for most experiments.

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4. Upgrading of the Tandem

(P. K. Den Hartog, C. E. Heath, and F. H. Munson)

A large number of tasks are carried out annually with theobjective of improving the performance and especially the reliability ofthe tandem. Many of these are difficult and time consuming but of littlegeneral interest. In this section, we mention only those that have themost important impact on the operation of the accelerator.

a. Computer Control and Monitoring of the Tandem

A program to monitor and eventually control the tandem with a

computer has been started. This work is likely to extend over a period of

years because of a shortage of funds and especially personnel to implement

the plans. At the present time, the emphasis is on monitoring all

important parameters of the machine. This work has already progressed far

enough to be very useful for day-to-day operation. An example of this is

the metering and recording of the tandem corona currents. Systematic

information of this kind is expected to point to incipient mechanical

and/or electrical problems.

All major subsystems of the accelerator will gradually be brought

under computer control as time and funds permit. During the past year, a

serial link between the terminal communication system and the computer-

based tandem-monitoring system was put into operation. Also, the foil

chamber in the terminal in now computer controlled.

b. West Injector

The control system for the new injector described in section

I.E.c. has been designed and some components have been acquired. The

control system will be installed in late FY 1983, after all exploratory

tests of the injector have been completed.

c. Control of Tandem-Terminal Voltage

Now that we are routinely accelerating beams with rather complex

mass spectra, the beam analyzer may lock on the wrong ion species when the

accelerator system is recovering from a tandem spark. This problem has

been largely eliminated by requiring the terminal voltage to return to its

original value before voltage control is returned to the beam analyzer.

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d. Focusing Lens in Terminal

Because of multiple scattering in the terminal stripping foil,

the heaviest ions accelerated by the tandem have a relatively poor

transmission. As part of the ATLAS project, an electrostatic quadrupole

triplet is being installed in the terminal to refocus the beam and hence

improve the transmission of the ion species of interest. This lens and its

control system are now in place and the system is ready for testing.

e. Foil Stripping

The effort to improve the lifetime and quality of stripping foils

is continuing. The primary effort at this time is to try to duplicate the

results of the Japan Atomic Energy Institute, where a new fabrication

procedure was reported to yield exceptionally long lifetimes. This work is

being carried out in collaboration with S. Takeuchi, an exchange visitor

from JAERI.

5. Ion-Source Development

(P. J. Billquist and J. L. Yntema)

This activity is aimed at developing improved negative-ionsources and specialized beams for use in the nuclear-physics program basedon the superconducting linac.

a. Ion-Source Test Facility

The new test facility which was just coming into initial

operation last year has been completed and extensively used to study

several kinds of sources. An emittance-measurement device has been added

to the system and is now in routine operation. The data provided by this

device is essential for a complete evaluation of a source, since it

indicates whether or not the output of the source can be efficiently

transmitted through the tandem.

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b. Inverted Sputter Source

The inverted sputter source with a new design, first described

last year, has by now been extensively studied and used on-line to provide

beams for the linac. Because of its high intensity, the source is able to

produce acceptable beams of low-abundance isotopes from sputter targets of

a number of natural elements. For example, in a recent nuclear-physics

experiment the unusual beam 5 0Ti was produced from natural titanium.

Experiments aimed at further enhancing the negative-ion yield of

the inverted sputter source are in progress, and preliminary data suggest

that substantial improvements may be feasible. Such an improvement would

be important to our experimental programs, since many beams of interest are

still too weak to be usable.

c. West Injector for the Tandem

A second ion-source position and injector for the tandem has been

designed, installed, and tested. The system performs well and is used

occasionally with the new source described in I.E.b. to provide special

beams for the experimental programs. The remaining task is to install the

electronics system required to control the ion source and injector in

routine operation.

d. The SNICS Source

The SNICS source (the U. of Wisconsin design) has recently been

modified to have internal optics that is similar to that in the ANL version

of the inversted sputter source (described in section I.E.b.). Preliminary

tests of the modified source suggest that it will have a somewhat greater

heavy-ion yield than the inverted sputter source for some ions. If so, it

will be very useful for some beams that are now too weak for the intended

application.

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e. Hydrogen Loading

For some ion-source target materials such as titanium, calcium,

and zirconium, the negative-ion yield can be enhanced by loading the target

with hydrogen. A loading chamber for this purpose has been built and put

into service. A series of tests have been carried out to learn how to load

targets reproducibly.

6. Near-Term Plans

a. Accelerator Operation

The level of funding in the President's Budget for FY 1984 will

allow the operation of the tandem-linac system to return to a six-day-per-

week schedule and it will also remove the need to shut down the operation

for long periods of time in order to reduce costs. This longer and more

regular schedule of operation will greatly increase running time.

Because of accelerator-improvement activities and the building

activities connected with the ATLAS project, there will continue to be some

interruptions in the accelerator operating schedule. However, these

interruptions will be unimportant until late 1984.

Outside users are expected to play an increasingly prominent part

in the research program at the superconducting linac. Consequently, we

plan to install a formal program of outside-user assistance, as is

discussed in Sec. V.7.

b. Linac Improvements

Most of the activities associated with the linac proper are now

more in the nature of maintenance than improvements. However, upgrading of

both the input and the output beam lines will continue to require effort.

In particular, we need to tackle the general problem of computer control of

beam lines, both because this capability is needed now and because

experience now will be valuable for ATLAS.

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c. Tandem Improvements

The main tasks through 1984 will be the following: (1) continue

computer monitoring and control of the accelerator, (2) complete the West

Injector, and (3) debug and refine the terminal lens. Completion of these

three projects will enhance operational efficiency and accelerator

capability to an important extent.

d. Ion Sources

There are two main elements to the near-terms plans for ion-

source development. One is the refinement of the inverted sputter source

and the SNICS (Wisconsin) source with the aim of improving efficiency and

ease of operation. Both sources, in their present form, have good basic

characteristics and are used to advantage to provide beams of interest to

the experimental program. However, both also have operational defects that

appear to have straightforward solutions. We will attempt to eliminate

these defects during the next year.

The second task will be to design a new East Injector for use in

ATLAS. One of the main objectives of the design will be to achieve better

mass resolution than is provided by either of the present injectors.

7. Assistance to Outside Users of the Superconducting Linac

The tandem-linac accelerator and its associated experimental

apparatus form a complex system that requires users to master a mass of

technical matters. Consequently, outside users need guidance and

assistance in order to work effectively. Until now, this assistance has

been informal. We propose to start a formal assistance program in FY 1984

by providing a wider range of assistance by a designated group of

individuals with continuing responsibilities.

Outside use of the superconducting linac has continued to

increase, both with respect to the number of persons involved and the total

amount of running time provided. In particular, the fraction of running

time allocated to outside users has increased from 3i% in FY 1982 to 51% in

FY 1983.

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The severely restricted funding level for FY 1983 in the heavy-

ion program requires that the total running time for FY 1983 be reduced

substantially below the FY 1982 level. This reduction, combined with the

increase in the number of outside users, is making it difficult to

accommodate all users under the present time-allocation policy, in which

all users are allocated time on a uniform basis. Consequently, we now

believe that the time has come to modify the policy, and this issue will be

presented for discussion at the next (second) meeting of the Policy

Advisory Committee. The first meeting of this committee was held in June

1982, at which time the committee recommended that our present informal

system of running-time allocation should be maintained as long as it

continued to work well.

The increased support for heavy-ion research in the President's

Budget for FY 1984 will permit the superconducting linac to be operated

much more intensively than in FY 1983, resulting in a substantial increase

in the availability of running time for outside users. Moreover, the

increasing degree of completeness of the experimental apparatus and

continuing refinements of the accelerator will make the facility a very

attractive one for research in precision heavy-ion research. Consequently,

by FY 1984, outside use of the superconducting linac will be a major

component in the national program for heavy-ion research, and this level of

effort requires that we start to implement a formal user-assistance

program.

Our present plan is to provide the following assistance for

outside users: (1) general liaison services, (2) instruction on the

characteristics of the accelerator system as a whole, (3) help in planning

experiments, particularly with regard to compatibility between the user's

equipment and the accelerator facility, (4) instructions on the use of

particular major apparatus that is part of the ATLAS facility, (5)

instruction and help with the use of computer hardware and software, (6) a

well-defined mechanism for making use of ANL facilities to solve unforeseen

technical problems, (7) some technical support in setting up experiments,

(8) office space, and (9) a minimal level of typing service.

The magnitude of the outside use of the accelerator during the

past year may be judged from the following two lists: (1) the experiments

194

performed by outside users and (2) the institutions represented. As may be

seen from the names associated with each experiment, the university groups

are by now playing a major role in an important fraction of the experiments

and a dominant role in some.

a. Experiments Involving Outside Users

All experiments in which outside users participated during the

period April 1982 to January 1983 are listed below. The names in

parentheses are Argonne collaborators.

(1) Development of a Laser-Spectroscopy Experimental ProgramM. A. Finn, G. W. Creenlees, and S. L. Kaufman, Univ. of Minnesota;R. M. Evans and D. A. Lewis, Iowa State Univ. (C. Davids)

(2) Spectroscopy of100CdL. Cleemann, C. Maguire, W. C. Ma, D. Cacic, and M. Barclay,Vanderbilt Univ. (T. L. Khoo, R. Janssens, D. Frekers, and P.Chowdhury)

(3) Measurement of K-Vacancy Equilibration Lengths in SolidsP. Cooney, Millersville State College (E. Kanter, D. Schneider, andB. Zabransky)

(4) Measurements of Nuclear States of 15 2YbY.-H. Chung, P. J. Daly, Z. Grabowski, J. McNeill, and M. 0.Kortelahti, Purdue Univ. (R. Janssens, P. Chowdhury, and T. L. Khoo)

(5) Tim-of-Flight Measurements of Evaporation Residues Produced in the 160+ Mg Reaction

J. J. Kolata, J. D. Hinnefeld, R. J. Thornburg, and R. J. Vojtech,Univ. of Notre Dame; F. W. Prosser, Jr., University of Kansas (D.Kovar, T. Humanic, R. R. Betts, P. Chowdhury, D. J. Henderson, R.Janssens, W. Kuhn, G. Rosner and K. Wolf)

(6) Accelerator Mass Spectroscopy of 44 TiB. Stievano, INFN, Legnaro (D. Frekers, W. Henning, W. Kutschera, K.E. Rehm, R. Smither, and J. Yntema).

(7) 3 7C1 Induced FusionF. W. Prosser, Jr., Univ. of Kansas (W. Freeman, W. Henning, D.Frekers, D. Geesaman, J. P. Schiffer, and B. Zeidman)

(8) Direct Reactions on 208PbM. Paul, Hebrew Univ., Jerusalem (K. E. Rehm, and W. Kutschera)

(9) Detection of High-Rydberg AtomsZ. Vager, Weizmann Institute (D. Gemmell, E. Kanter, and D.Schneider).

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(10) Accelerator Mass Spectroscopy of 41CaM. Paul, Hebrew Univ.; X. Ma, Institute of Atomic Energy, Peking (W.Kutschera, D. Frekers, K. E. Rehm, R. Smither, and J. Yntema)

(11) Investigation of 186Hg Isotaeric StateP. J. Daly, Z. Grabowski, Y.-H. Chung, J. McNeill, M. 0. Kortelahti,Purdue Univ. (R. Janssens, D. Frekers, P. Chowdhury, and T. L. Khoo)

(12) Shape Change in 155ErG. Bastin, C. Schuck, CNRS, Orsay; F. Beck, CNRS, Strasbourg; M. 0.Kortelahti, Purdue Univ. (R. Janssens, T. L. Khoo, W. Kuhn, and D.Frekers)

(13) Lifetime Measurements on the 15 8Er* SystemH. Emling, GSI, Darmstadt; R. J. Broda, Y-H Chung, P. J. Daly, Z. W.Grabowski, M. 0. Kortelahti, J. McNeill, Purdue Univ. (P. Chowdhury,W. Kuhn, T. L. Khoo, R. Janssens, and G. Rosner)

(14) Inelastic and Single-Nucleon Transfer for 160 on 40CaJ. J. Kolata, R. J. Vojtech, Univ. of Notre Dame (D. Kovar, R. Pardo,K. E. Rehm, G. Rosner, and H. Ikezoe)

(15) Tusion with 40Ca BeamsH. A. Al-Juwair, R. J. Ledoux, M.I.T. (R. R. Betts, and S. Saini)

(16) Fission and Fast Fission for the Systems 19F, 2 4Mg, 28Si and 208PbC.-K. Gelbke, B. Tsang, W. G. Lynch, H. Utsunomiya, Michigan StateUniv.; P. A. Batsden, M. A. McMahan, Lawrence Livermore Laboratory(B. Back and S. Saini)

(17) Very High Spin States in 147GdJ. Borggreen, G. Sletten, Niels Bohr Institute; R. J. Broda, Y.-H.Chung, P. J. Daly, Z. W. Grabowski, M. 0. Kortelahti, and J. McNeill,Purdue Univ. (P. Chowdhury, R. Janssens, T. L. Khoo, D. Frekers, andW. Kuhn)

(18) Isomers in N = 82 NucleiR. J. Broda, Y-H Chung, P. J. Daly, Z. W, Grabowski, M. 0.Kortelahti, and J. McNeill, Purdue Univ. (T. L. Khoo, R. Janssens,and P. Chowdhury)

(19) Two Electron Titanium WavelengthsA. E. Livingston, Univ. of Notre Dame (H. G. Berry, J. Hardis, and W.Ray)

(20) Structure of Hg IsotopesR. J. Broda, Y-H Chung, P. J. Daly, M. 0. Kortelahti, Z. Grabowski,and J. McNeill; (R. Janssens, T. L. Khoo, and D. Frekers)

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b. Outside Users and Institutional Affiliations

(1) Michigan State UniversityD. A. ArdouinC.-K. GelbkeW. G. LynchB. TsangH. UtsunomiyaZ. Xu

(2) Purdue UniversityR. J. BrodaY.-H. ChungP. J. DalyZ. W. GrabowskiM. O, KortelahtiJ. McNeill

(3) Notre Dame UniversityJ. D. HinnefeldJ. J. KolataA. E. LivingstonR. J. ThornburgR. J. Vojtech

(4) Vanderbilt UniversityM. BarclayD. CacicL. CleemannW. C. MaC. Maguire

(5) Iowa State UniversityR. M. EvansD. A. Lewis

(6) University of KansasF. W. Prosser, Jr.

(7) Lawrence Livermore LaboratoryP. A. BaisdenM. A. McMahan

(8) M.I.T.H. A. Al-JuwairR. J. Ledoux

(9) University of MinnesotaM. A. FinnG. W. GreenleesS. L. Kaufman

(10) Millersville State CollegeP. Cooney

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(11) U. S. Naval AcademyT. Humanic

(12) CNRS, OrsayG. A. BastinC. Schuck

(13) CNRS, StrasbourgF. Beck

(14) University of CopenhagenJ. BorggreenG. Sletten

S. Bjdrnholm

(15) G.S.I., DarmstadtH. Emling

(16) Hebrew University, JerusalemM. Paul

(17) INFN, Legnaro (Italy)B. Stievano

(18) Weizmann Institute

Z. Vager

(19) Institute of Atomic Energy, Peking, P.R.C.X. Ma

c. Summaries of Major User Programs

Several groups listed in the above tables have embarked on

extensive research programs that are likely to make use of the tandem-linac

accelerator for several years. In order to give some indication of the

extent of these efforts, the following descriptions summarize the research

of five groups that have been most active during the period April 1982 to

March 1983.

i. The Purdue University Group (P. J. Daly, Z. Grabowski, Y. H. Chung,

S. R. Faber, H. Helppi, M. Kortelahti, A. Pakkanen, J. McNeill,

and J. Wilson)

The Purdue University group has an active program on high-spin

nuclear states at the linac. The personnel currently includes two

professors, one visiting scientist from Poland, one post-doc, and three

graduate students. One student whose thesis was largely based on work

198

conducted at the linac has already graduated. A second student, whose work

was entirely based on linac experiments, will soon complete his thesis.

Our program uses in-beam Y-ray techniques and is directed at

several aspects of nuclear structure at high spin. We are testing the

validity at the Z = 64 sub-shell closure through spectroscopic studies of N

= 82 nuclei close to the proton drip line. This past year a 40-us 10+

isomer was discovered in t7Yb82 which, having a half-filled proton h1 1 /2

shell, was predicted to have a long-lived isomer. By studies on N = 87 and

88 Dy isotopes we are also investigating the transition between oblate

aligned-particle and prolate-collective structures as a function of both

spin and neutron number. Evidence for a prolate-to-oblate shape change has

been found in 153,154Dy. Studies in 186Hg have revealed for the first time

decoupled vi1 3/ 2 bands with both prolate and oblate shapes.

The program is conducted in close collaboration with the Y-ray

group at Argonne and details may be found elsewhere in this document.

We have begun a project to construct a superconducting solenoid

lens to be used as a conversion-electron spectrometer. The solenoid has

been delivered by the manufacturer and the magnetic field profile has been

determined to be within specifications. The spectrometer is currently

being assembled at Purdue and, after testing there, will be installed at

Argonne late in 1983. A lens spectrometer, on loan from the University of

North Carolina and Oak Ridge National Laboratory, has been prepared for on-

line use in the interim period.

ii. University of Kansas Collaboration (F. W. Prosser, Jr.)

Heavy-ion reaction mechanisms are being studied by observing the

partition of reaction cross section and its dependence on energy and

neutron excess. Fusion-fission,. fusion-evaporation, and deep inelastic

scattering for 32S projectiles incident on targets of 112,116,120,124Sn

were studied over the energy range 130-247 MeV. In a search for entrance-

channel effects in the formation of compound systems, the even-A Sn

isotopes 112-1 1 4 Sn were bombarded with beams of 58Ni and 64Ni at laboratory

energies that varied from 230 to 322 MeV. In these measurements, the

influence of neutron excess (for both target and projectile) upon the

fusion-evaporation yields was emphasized.

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In addition, the energy dependence of fusion and incomplete

fusion processes for lighter systems involving 28Si have been studied. In

a search for incomplete momentum transfer (i.e., incomplete fusion),

velocity spectra were measured for individually-resolved evaporation-

residue masses produced in reactions of 28Si projectiles at Elab >, 260 MeV

on targets of 12 C, 24Mg, 2 4Al, 28Si, and 4 0 Ca. Also, in order to

investigate the role of entrance-chanrel effects, evaporation-residue cross

sections were measured for the reactions 28Si + 28Si and 160 + 40Ca, which

form the same compound nucleus 5 6Ni. The 2 8Si + 28Si system displays

significantly smaller cross sections at higher energies than does 160

+ 40Ca. Further investigations of this effect are planned.

iii. MSU and LLL Collaboration (C. K. Gelbke, W. Lynch, M. S. Tsang,

Z-Xu, P. Baisden and M. McMahan)

The properties of fission fragments from the 32S + 20 8Pb reaction

have been studied in detail. These studies include measurements of cross

sections, angular distributions, fragment masses, and folding-angle

distributions at projectile energies of 180-270 MeV. This study shows that

compound-nucleus formation is strongly suppressed for this reaction system

even at the lowest bombarding energies, with a major fraction of the cross

section going to the quasi-fission reaction. In a subsequent experiment,

which is presently being analyzed, we have measured angular distributions

for 19F, 24Mg, 2 8Si + 20 8Pb reactions over a range of beam energies in an

attempt to localize the onset of quasifission, which is known to be absent

in the 160 + 2 08Pb reaction and dominating in the 32S + 2 08Pb reaction.

In the next experiment we plan to measure the neutron emission

from the 32S and 2 0 8 Pb reaction with the aim of determining the ratio of

pre- to post-fission neutrons. It is anticipated that such measurements

will be helpful in determining the time scale of the quasifission reaction,

a quantity which is of central importance for the development of a better

understanding of heavy-ion reaction dynamics involving large mass

transfers.

200

iv. Iowa State and Minnesota Collaboration (D. A. Lewis, R. M. Evans,

G. W. Greenlees, and S. L. Kaufman and M. A. Finn)

This project will 'se on-line laser spectroscopy to study the

optical hyperfine structure of radioactive atoms. The objective is to

extract information on spins, moments, and the variation of charge radii

for ground states and isomers. The species under investigation will be

produced by heavy-ion beams fromthe tandem-linac. The radioactive atoms

recoil from the production target, become thermalized in a helium

atmosphere, and then are transported by a liquid-nitrogen-cooled helium jet

to the laser interaction region. Resonance fluorescence spectroscopy will

be employed to observe the optical transitions. Essentially Doppler-free

linewidths will be obtained by collimating the atoms into an atomic beam as

they emerge from the helium jet. Two cooled photomultiplier tubes will

detect the fluorescent light.

The linac target station for the cryogenic helium jet has been

completed. Tests using the linac beam have been conducted, indicating

copious production of the Ba radionuclides using the 12 2Sn(1 2C,xn)1 3 4-xBa

reactions. The skimmer efficiency for Ba is 2.5%, slightly higher than

that obtained for lighter As, Ge, and Ga isotopes. A large blower pump has

been installed, which should lead to better cooling of the atomic beam upon

emergency from the capillary. The laser beam transport system between the

laser laboratory and the cryogenic helium jet has been installed. Tests to

reduce the background of scattered laser light will begin soon. It is

probable that measurements with a complete system will begin in the summer

of 1983.

v. University of Notre Dame (J. Kolata, J. Hinnefeld and R. Vojtech)

We have participated in studies of the energy dependence of

fusion and incomplete fusion cross sections for reactions induced by 160

and 2 8Si projectiles. Velocity spectra of individually-resolved

evaporation-residue masses produced in 160 + 12C, 2 4 Mg, and 40Ca reactions

at Elab(1 60) < 150 MeV and 2 8Si + 12C, 2 4Mg, 2 7A1, 2 8Si, and 40Ca reactions

at Elab(2 8Si) < 260 MeV were measured by means of time-of-flight

techniques, and the results were compared with theoretical predictions for

201l

complete fusion. Evidence for incomplete momentum transfer (i.e.,

contributions from incomplete fusion) was observed at the higher bombarding

energies for some systems, but not for others. Further investigations of

this projectile-target dependence are planned. As a part of a study of the

energy dependence of reactions induced by a variety of projectiles on 40Ca

and 2 0 8 Pb, the cross sections for elastic and inelastic scattering and for

transfer reactions were measured for the 160 + 4 0Ca system at Elab( 1 6 0)

150 MeV. The angular distributions will be compared to the predictions of

DWBA and CCBA to test the adequacy of the calculations at the higher

bombarding energies.

203

B. OPERATION OF THE DYNAMITRON FACILITY

The Physics Division operates a high-current 4.5-MV Dynamitron

accelerator which has unique capability as a source of ionized beams of

most atoms and many molecules. Among the unusual facilities associated

with the Dynamitron are (1) a beam line capable of providing

"supercollimated" ion beams permitting angular measurements to accuracies

of 0.005 degree, (2) a beam-foil measurement system capable of measuring

lifetimes down to a few tenths of a nanosecond, (3) an experimental system

dedicated to measuring absolute nuclear cross sections at low energy, (4) a

variety of experimental apparatus for weak-interaction studies, (5) a

simultaneous irradiation system by which heavy ions from the Dynamitron and

helium ions from a 2-MV Van de Graaff accelerator are focussed on the same

target, (6) a post-acceleration chopper system giving beam pulses of

variable width from about one nanosecond to the millisecond range at

repetition rates variable up to 8 MHz, (7) a scattering chamber for

electron spectroscopy with electrostatic parallel-plate electron

spectrometers with variable energy resolution (0.1% to a 5%) and the

capability to measure electron energies up to a few keV as a function of

observation angle, and (8) a McPherson electrostatic spherical electron-

spectrometer system capable of measuring electron energies with high

precision and very high efficiency. A PDP-ll/45 computer system is used

for on-line data analysis and for the control of experiments.

1. OPERATIONAL EXPERIENCE

B. J. Zabransay, D. Schneider, R. L. Amrein, and A. E. Ruthenberg

Overall, the Dynamitron continued to perform well during the past

year. The normal operating schedule was twenty-four hours a day, five days

a week. Very little running was done on weekends during calendar year

1982.

During the year the accelerator was staffed a total of 5380

hours. Of this time 4729 hours (88%) were scheduled for experimental

research during which a beam was provided to the experimenters 90% of the

time. Machine preparation time used up 6% of the scheduled research time

204

and machine malfunctions 4%. Scheduled accelerator improvements (including

the upgrading program) and modifications used a total of 651 hours or 12%

of the total available time.

The great versatility of the Dynamitron continued to be exploited

by the research staff. Ion currents on target varied from less than a

nanoampere to about 100 microamperes with ion energies ranging from 0.2 to

4.0 MeV. A wide range of both atomic and molecular ions was delivered on

target. They included 1H+, 1H + 2H+ 1H + 3 He+, 2H2+ 4He+ 4HeH+ 2H3+,

7L + 7L +, 7Li , 12C+ 14N 4 1N++, 28e+ 20Ne++, 4 N +40Ar+Ni N LiNe,2'40Ar++ 40Ar+++

During the year a total of 55 investigators used the Dynamitron

in some phase of their experimental research. Of these, 12 were from the

Physics Division, 10 were from other Argonne research divisions, 21 were

outside users from other research facilities, 9 were members of the

Resident Graduate Student Program, and 3 were undergraduate students

participating in research at the Dynamitron. Of the scheduled time, 89%

went to experiments involving members of the Physics Division, 10% to other

Argonne divisions, and 1% was exclusively assigned to outside users.

However, outside users collaborated in experiments that used 66% of the

total available time. Undergraduate students and participants in the

Resident Graduate Student Program worked on experiments that used 77% of

the time.

The accelerator has been heavily used by several research groups

during 1982. It has been operating with only routine maintenance problems

and relatively free of sparking for voltages up to 4 MV. Sparking above 4

MV is still a problem. The terminal control rods continue to be damaged

even with special modifications. Early in 1983 the accelerator tube will

be reoriented to try to correct this problem. A system to eliminate the

control rods by the use of fiber-optic or infrared light-link control of

stepping motors is being studied. Step-by-step improvements to the various

machine components and configurations will be made as tests of the maximum

energy-holding capability continue.

The fiber-optic light-link system for monitoring electrical

parameters within the high-voltage terminal was damaged again by a series

of sparks when the machine was operating in the 4-MV range. The fiber-

optic bundle was removed to allow operation at higher energies. It will

again be installed after being repaired and after the accelerator tube is

reoriented. The bundle will be repositioned on the column so as to reduce

damage.

205

Two beam lines were changed this year. One was built up to allow

experiments using a McPherson electron spectrometer. A scattering chamber

for electron spectroscopy was added to another beam line. The experimental

area was improved with a large increase in the ambient light and a general

organization of the area. Various vacuum improvements were made to several

of the beam lines.

The development of ion sources to provide ion species of interest

to specific experimental groups has proceeded slowly during the year

because of the decrease in the number of technical staff. A beam of Li+

can now be produced easilyand was used many times during the year. With

only a minor modification, it is hoped that a Be+ beam can be produced from

the same source. A Penning source is being modified to accept cathodes

made of Si in order to produce a Si+ beam. The machining of the Si uses a

special process and is being done by the Dynamitron technical staff.

A Capillaritron ion source is under development. It uses a

nozzle with a 25-micron orifice. When gas flows through the nozzle and it

is biased at 2 to 15 kV, a plasma forms just inside the tip, producing

copious quantities of various ions. Initial tests are encouraging but many

problems, including poor focussing and a high gas load on the accelerator

tube, will have to be overcome.

2. UNIVERSITY USE OF THE DYNAMITRON

B. J. Zabransky

The Argonne Dynamitron continues to be a valuable research

facility for scientists from outside institutions. It is not only the

accelerator itself that attracts outside investigators but also the unique

associated experimental equipment as well as the on-going research program

being conducted at the Dynamitron.

Most visiting scientists chose to collaborate with local

investigators on problems of common interest. A few, however, worked as an

independent group. Some came for a one-time-only experiment, but most are

participants in research programs that have spanned a period of several

years.

During the year twenty-one scientists came from thirteen outside

institutions to use the Dynamitron. They came from eight states and three

foreign countries. They participated in experiments that used 66% of the

time scheduled for research. A list of those institutions from which users

of the Dynamitron came during 1982 is given below. The list includes the

206

name of the institution, the title of the research project, and the names

of the principal investigators. The names of their Argonne collaborators

are enclosed in parentheses.

(1) Arizona State UniversityDevelopment of Capillaritron Ion Source

J. Kelly, (D. S. Gemmell)

(2) University of Freiburg, Berlin, West GermanyElectron Spectroscopy of Fast-Ion CollisionsUsing Simultaneous Laser Excitation

R. Bruch, (D. Schneider, W. St6ffler, V. Pfeufer,B. Zabransky, H. G. Berry, and P. Arcuni)

(3) Fudan University, Shanghai, ChinaInfluence of Rydberg States in Convoy Electron Measurements

Gu Yuan Zhuang, (D. S. 2emmell, E. P. Kanter,D. Schneider, Z. Vager, and B. J. Zabransky)

(4) Marquette UniversityRadiation Damage of Covalent Crystal Structures

L. Cartz, A. Gowda, F. G. Karioris,and T. Ehlert

(5) Northwestern UniversityDirect Capture in the 2 7 Al(p,Y) and

R. E. Segel, E. Zupranska,* G.(A. J. Elwyn, and W. Ray)

1 9 F(p,Y) ReactionsHardie,* M. Wiescher,*

(6) University of Notre DameSpectra of High Spin States in Light Elements

A. E. Livington, (H. G. Berry, J. Hardis, and W. Ray)

(7) Ohio State UniversityDirect Capture in the 2 7 A&(p,Y) and

M. Wiescher, G. Hardie,* R. E.(A. J. Elwyn, and W. Ray)

1 9 F(p, Y) Reactions

Segel,* E. Zupranska,*

(8) University of TexasAutoionization Electron Spectroscopy of Li, He, Ne, and Ar

C. F. Moore, P. Seidel, (D. Schneider, P. Arcuniand W. Stoffler)

(9) University of ToledoMeasurements of Forbidden Transition Rates

P. S. Ramanujam, L. Curtis, (H. G. Berry,J. Hardis, and W. Ray)

(10) Valp raiso UgiversityThe Li(d,p) Li Reaction and Solar Neutrino Capture Rates

D. Koetke, (B. Filippone, A. J. Elwyn, and W. Ray)

*From another outside institution.

207

(11) Weizmann Institute, Rehovot, Israel

Studies of Beam-Foil Excited Rydberg AtomsZ. Vager, (D. S. Gemmell, E. P. Kanter, D. Schneider,and B. J. Zabransky)

(12) Western Michigan Univerity 19Direct Capture in the AI(p,Y) and F(p,Y) Reactions

G. Hardie, R. E. Segel,* M. Wiescher,* E. Zupranska,*A. J. Elwyn, and W. Ray)

(13) Yale UniversityMicrowave Field Ionization of Foil-ExcitedFast Rydberg Atoms

P. Koch, D. Mariani, W. van de Water, (D. S. Gemmell,E. P. Kanter, D. Schneider, and B. J. Zabransky)

The Resident Graduate Student Program is open to students that havefinished their course work and passed their prelims. They come to Argonneand perform their Ph.D. thesis research here. Nine members of this programworked at the Dynamitron during 1982. Altogether they participated inexperiments that used 77% of the time allotted to research. Those who usedthe accelerator are listed below, together with their home university andtheir local thesis advisor.

(1) P. W. Arcuni, University of ChicagoH. G. Berry, advisor

(2) R. Evans, Iowa State UniversityC. N. Davids, advisor

(3) B. Filippone, University of ChicagoC. N. Davids, advisor

(4) M. Finn, University of MinnesotaC. N. Davids, advisor

(5) C. A. Gagliardi, Princeton UniversityG. T. Garvey, advisor

(6) J. Hardis, University of ChicagoH. G. Berry, advisor

(7) A. R. Heath, University of ChicagoG. T. Garvey, advisor

(8) W. Stbffler, Free University of BerlinD. Schneider, advisor

(9) G. Zapalac, University of ChicagoH. G. Berry, advisor

*From another outside institution.

208

In addition, the following undergraduate students have participated inresearch based at th Dv'iamitron.

(1) J. Bales, North Carolina State UniversityD. S. Gemmell, advisor

(2) J. J. Hofmann, East Stroudsburg State CollegeD. Schneider, advisor

(3) J. E. Tkaczyk, Rutgers UniversityE. P. Kanter, advisor

2091,1

VI. DATA ACQUISITION AND ANALYSIS SYSTEMS

A. ON-LINE

The construction of a new accelerator (ATLAS) has provided the

opportunity to examine critically the future needs of the Division with

respect to data acquisition and has led to the conclusion that the present

system based on PDP 11/45's with the operating system DOS could not fulfill

the anticipated needs. Hence, for the moment, the present on-line data-

acquisition systems are being only maintained and no extensive development

effort is planned for them.

B. OFF-LINE

The VAX 11/780 is proving to be very useful for analysis and is

being used for an ever-increasing variety of purposes. To enhance its

capability a 6250 bpi, 125 ips magnetic tape unit was ordered (and as of this

writing, installed); an additional 1.5 Mb of memory was likewise installed

thus bringing the total memory to 5 Mb; and lastly, a floating-point

accelerator has been ordered and received but not yet installed.

C. FUTURE

A project has been initialized to provide for the data-acquisition

systems needs for the future. The project (called DAPHNE, for Data-

Acquisition by Parallel Histogramming and NEtworking) involves parallel

processors to histogram buffers of events before passing them to the main

acquisition computer. The project is now into its planning phase and

feasibility studies are being performed.

2111/1.

AEOMIC AND MOLECULAR PHYSICS RESEARCH

Introduction

The Atomic Physics research in the Physics Division currently consists ofthe following six ongoing- programs:

(1) Photoionization-photoelectron research (J. Berkowitz),

(2) High-resolution laser-rf spectroscopy with atomic and molecular beams(W. J. Childs and L. S. Goodman),

(3) Beam-foil research and collision dynamics of heavy ions (H. G.Berry),

(4) Interactions of fast atomic and molecular ions with solid and gaseous

targets (D. 3. Gemmell and E. P. Kanter),

(5) Theoretical atomic physics (K. T. Cheng),

(6) Electron spectroscopy with fast atomic and molecular-ion beams

(D. Schneider).

Major new opportunities that we see for our work in the near future lie inextension of the rf-laser double resonance work to atomic and molecularions, the use of VUV lasers in studies on the photodissociation ofmolecular ions, and at the Dynamitron, further studies with fast molecular-ion beams and the spectroscopy of few-electron heavy-ion systems.

During FY 1981 and FY 1982 we have been fortunate in having, as a visitingscientist from the Hahn-Meitner Institute (Berlin), Dr. Dieter Schneider, aphysicist who has specialized for several years in accelerator-based atomicphysics and in electron spectroscopy in particular. Beginning February 1,1982, Dr. Schneider joined the permanent staff of the Physics Division.Beginning in FY 1983, Dr. Schneider became the Principal Investigator in anew program of electron spectroscopy based at the Dynamitron. His programintegrates into and complements nicely the other existing programs inAtomic Physics in the Physics Division. Together, the three programs inphysics with fast molecular ions, beam-foil spectroscopy, and electronspectroscopy account for about 75% of the beam time available at theDynamitron.

Already we have seen some fruits from the symbiotic nature of theseprograms. The recent discovery at the Dynamitron of the previouslyunrecognized role of 'ydberg atoms in convoy-electron studies is a goodexample.

During FY 1982, Dr. H. G. Berry was on overseas leave for 9 months. Hespent 6 months at the Laboratoire Aim Cotton, Orsay, France, and 3 monthsat the University of Lund, Sweden.

213

VII. PHOTOIONIZAT ION-PHOTOELECTRON RESEARCH

Introduction

Our photoionization research program is aimed at understanding-the basic processes of interaction of light with molecules, the electronicstructures of molecules and molecular ions, and the reactions of molecularions, both unimolecular and bimolecular. The processes and species westudy are implicated in a wide range of chemical reactions, and are ofspecial importance in outer planetary atmospheres and in interstellarclouds. Our work also provides fruitful tests for theories of electronicstructure, which help in the evaluation of widely applicable models formulti-electron systems. Most of this work is of a fundamental nature, butwe also use the precise methods developed here to determine thermochemicalquantities (heats of formation and ionization potentials) directly relevantin, e.g., reactions with ozone in the stratosphere, possible side reactionsin a magnetohydrodynamic generator and reactions in interstellar clouds.Our experimental studies utilize five pieces of apparatus - twophotoionization mass spectrometers and three photoelectron energy analyzers- each with special features.

(1) A three-meter normal-incidence vacuum-ultravioletmonochromator combined with a quadrupole mass spectrometer. This apparatusis capable of the highest resolution currently achieved in photoionizationstudies. It is also convenient for investigation of wavelength-dependentphotoelectron spectra.

(2) A one-meter normal-incidence VUV monochromator mated with amagnetic-sector mass spectrometer. This apparatus has higher massresolution, is less discriminatory in relative ion-yield measurements, andcan be used to study metastable ions. Higher intensity for weak signalscan also be achieved.

(3) Two cylindrical-mirror photoelectron-energy analyzers, whichaccept a large solid angle of photoelectrons, close to the "magic angle" of54*44'. One has been extensively used for the determination of thephotoelectron spectra of high-temperature species in molecular beams, andthe other has on occasion been mated with the three-meter monochromator forstudies of photoelectron spectra as a function of wavelength.

(4) A hemispherical electron-energy analyzer incorporated in achamber which permits one to rotate the analyzer over a substantialfraction of 4n. This device is intended for angular-distributionmeasurements, and also enables us to study very-high-temperature species.

The experiment involving UV laser photodissociation of molecular

ions has progressed to the point where photofragment signals can be readilydetected, without long searches. In the near future, the magnetic massspectrometer will be dedicated to this work.

One year ago, the interfacing of a multitask minicomputer withour experimental apparatuses was incomplete. Only the photoionization massspectrometric experiment was minicomputer controlled. Now thephotoelectron apparatus and the laser photodissociation experiment are alsocomputer interactive, the latter employing a serial highway and driver.

214

The experiment involving- UV laser photodissociation of molecularions advanced one more stage. A quadrupole mass spectrometer wasincorporated to select the mass of the primary molecular-ion beam. The

problems anticipated with this addition, involving- a quadrupole source andelectronics floating at high voltage, were overcome without greatdifficulty. In the forthcoming year, major challenges are expected when amultichannel array detector is introduced, together with a new laser adRaman shifter.

An important practical achievement was the production of atomicchlorine, and its transportation to the interaction region without rapidrecombination and loss. Similar techniques should enable us to examineother transient species.

Other technical progress included:

(1) The completion of an extensive photoelectron experimental

study on the lanthanide trihalides, using both the He I (584 %) and He II(304 A) incident radiation. The relative binding- energies of 4f-like andligand-like orbitals were clearly revealed in these experiments.

(2) The initiation of photoelectron spectroscopic studies on a

class of Group III metal oxides, including Ga20, In20 and B202 .

(3) The attainment of a photoionization spectrum of atomicchlorine, from ionization threshold at ~ 956 A to ~ 750 A. Autoionizationresonance features converging to P, 1 D2 aad ISo ionic limits were clearlyseen, with good resolution (0.28 0).

(4) UV laser photodissociation studies were made on severalmolecular ions. The experiments measure kinetic energy release in thecenter of mass, both by time-of-flight velocities and by momentumanalysis. Good agreement has now been achieved between these twomethods. These experiments are detailed below.

a. Photoelectron Spectra of the Lanthanide Trihalides and their

Interpretation (B. Rusci6, G. L. Goodman and J. Berkowitz)

The He I photoelectron spectra of gaseous LaCi3 , LaBr3 , LaI3 ,

CeBr3 , CeI3 , NdBr3 , Nd1 3 , Ern3 , LuBr3 and LuI3 have been obtained. They

display apronounced increase in splitting, and hence a progressively

clearer definition of peaks in the valence band as either the halogen or

the lanthanide increases in atomic number. These experimental features,

together with a refined relativistic Xa DVM calculation using the

von Barth-Hedin potential, have enabled us to assign these peaks with

confidence. The He II photoelectron spectra of CeBr3 , NdBr3 and LuI3 were

also obtained. They reveal that the 4f-like ionizations of early

215

9 10 II 12 13IONIZATION ENERGY (eV)

liii III(b) CeBr

"" I'.

D.. -

CD - -

8 9 10 11 12 13IONIZATION ENERGY (eV)

20

1500

V)

z

LU

H? 1000Z0

I-0-JWo 50000

I-

24O

-V00

1111 III

(a) CeBr3

iey0

0 -0

*

0 00 -0

I '1*

9 IC II 12 13IONIZATION ENERGY (eV)

(d) LuI3

" N V ,. _

8 12 14 i16IONIZATION ENERGY (ev)

14 15

Fig.VII-l. The 21.2-eV photoelectron spectrum of an early lanthanide,CeBr in (a) displays the halogen p-like valence band. The 40.8-eVspectrum in (b) reveals an additional peak at lower ionization energy(%9.6 eV), attributable to a 4f-like ionization. The 21.2-eV spectrumof a late lanthanide. LuI3 , is displayed in (c), and shows enhancedsplitting. The 40.8-eV spectrum of LuI3 in (d) has additional peaks dueto 4f-like ionizations, but at much higher energy (4l6.2 and 17.7 eV)than the valence band. Calculated energies are indicated by tick marksat the top of each figure.

n.

(c) LuI 3

0

I *

iOi/

J 0 0- 8

4

H

z

z

z 200

-JW0

OHI

rc

0

Z 6CH

-J00 7

ij hc

216

lanthanide members (e.g. Ce) occur at lower energy than the ligand valence

band, but that those of late members (e.g. Lu) are core-like. The

aforementioned calculations reproduce this behavior quantitatively. They

also help to rationalize a bi-modal behavior in the valence band; the

spectra with the 4f shell less than half-filled are very similar, as are

those with the 4f shellmore than half-filled, but the two groups are

distinctly different. The width of the valence bands, which varies over a

factor 2.5, is correctly reproduced. The calculations have been extended

to include fluorides. Both the calculations and available experimental

comparisons yield a picture in which the lanthanide fluorides display

predominantly ionic bonding (Ln2 .2 +); the bonding takes on successively

more covalent character as one proceeds to chlorides (Ln1.6 +), bromides

(Ln1.3+) and iodides (Lnl.0+). (See Fig. VII-1.)

b. Photoelectron Spectra of Metal Oxide Vapors of Group III(B. Ruscit, G. L. Goodman, and J. Berkowitz)

The metal oxide vapors M2 0 (M = Al, Ga, In, T) have been studied

mass spectrometrically, by electron diffraction and by matrix isolation

infrared spectroscopy. Their structure (bent or linear) is still not

certain. We have obtained He I photoelectron spectra of all the above

species except A1 2 0, and have used Xa DVM calculations to interpret these

spectra. Our results cannot be used to distinguish geometric structures,

but they do shed light on the orbital composition of these species.

In each instance, the band at lowest ionization energy is rather

narrow, and is followed by broader bands. The energy separation between

narrow and broad features decreases as the metal atomic number increases.

This pattern was previous]; observed in the PES of Group III metal

monohalides. The ionic bonding model which was used to interpret those

spectra appears to be applicable here as well. In that model, the narrow

lowest-energy peak was attributed to ionization from a molecular orbital

largely composed of metal s and p orbital. The Xa DVM calculations

support this interpretation for the metal oxides except for T 2 0, where the

calculations indicate that this orbital has acquired a large 0 2p

character. There are additional discrepancies between the experimental PES

217

of T920 and the corresponding- calculations which we are currently trying- to

resolve.

c. Photoelectron Spectrum of B02 (B. Rusci6, L. A. Curtiss,*and J. Berkowitz)

It has been known for some time that the gaseous species B2 02 is

generated when a mixture of boron and B2 03 is heated to ~ 1200 C. We have

examined this species effusing from an oven by VUV photoelectron

spectroscopy, using- the He I resonance line as incident radiation. We have

thus far observed four peaks, with maxima at 13.62, 14.45, 15.33 and 15.85

eV. Hartree-Fock calculations clearly indicate that the most stable

neutral molecular structure is 0-B-B- less 0. The linear structures B-0-B-

0, B-0-0-B and the planar rectangle are stable by 1.8, 9.2 and 12.3 eV,

respectively. Furthermore, the calculated orbital energies of 0-B-B-0 are

the only ones that closely approximate the observed energies.

Vertical ASCF energies calculated with a 4-31 G basis set yield

13.72, 14.63, 16.16 and 16.50 eV for the four lowest energy ionizations,

which correspond to electron ejection from i ,ru, ag. and au orbitals,

respectively.

The structure 0-B-B-0 is isoelectronic with the stable cyanogen

structure NEC-C=N. However, the orbital sequence exhibited in the PES of

C2N2 is clearly different. There, the two sharp peaks characteristic of

ionization from a orbitals occur at energies intermediate between the Wg.

and lru ionizations. In both cases, vibrational excitation is observable in

the bands resulting from it orbital ionizations, which are also the ones

having the largest area. This provides additional confirmation for our

assignments.

*Chemical Engineering'Divisio'.t, ANL.

c. Photoelectron Spectrum of ALF (J. Berkowitz)

In the course of trying- to prepare CaF vapor for photoelectron

spectroscopic study, aluminum metal and CaF2 were combined and heated. For

reasons now well understood, CaF was not generated but instead a highly

218

satisfactory spectrum of the previously unexplored ALF was obtained. Its

spectral pattern fits well with those of other Group III monohalides (TLX,

InX) previously studied in this laboratory.

e. Photoelectron Spectra of BiX3 and BiX (G. Jonkers* and J. Berkowitz)

A combination of single-oven experiments to generate Bi 3 and

BiBr3 vapors, and double-oven experiments in which these vapors were

permitted to react with independently heated bismuth have succeeded in

generating the trihalide and monohalide independently. An unequivocal

interpretation of the results must await the completion of these

experiments.

*Netherlands-U.S. Exchange Fellow, Fulbright Program.

f. Photoionization of Atomic Chlorine (B. Ruscit, J. P. Greene,

and J. Berkowitz)

Chlorine has become a test case for ab initio theories of the

photoionization of open-shell atoms. In order to incorporate

autoionization resonances, a many-body theory (MBT) is required. An

experimental result is essential for testing these theories.

For this experiment, atomic chlorine is generated in a microwave

discharge. Recombination of these atoms is largely prevented by coating

the reactor wall with an appropriate agent. The photoionization experiment

is performed with the use of a three-meter monochromator and quadrupole

mass spectrometer.

The photoionization spectrum displays some resonance features

converging to 3P1, three prominent series (one broad and two narrow)

converging on 1D2 and two series converging on 1S0. Of the two

calculations (R-matrix and diagrammatic MBT) recently published which

attempt to predict the resonant structure, the latter comes much closer to

the experimental observations, both in terms of quantum defects, peak

shapes and absolute intensities. However, a major discrepancy even here is

the appearance of two narrow series converging on 1D2 , where only one is

predicted in the calculation. (See Fig. VII-2.)

219

d' l5d'

7s~8s6d"

ti

1

7s5d 6c 8s

i 7d

9s

' I6

6s

13.5 14.0PI0T0N ENERGY (eV)

h

(a)look-Fig. VII-2. A portion of

the photoionizationspectrum of atomicchlorine obtained in thecurrent experiments isshown in (a); a spectrumof the same regioncalculated by Brown et al.1

using diagrammatic many-body perturbation theory,is shown on a commonenergy scale in (b). Theshapes of the "d" and "s"

series features isreproduced in thecalculation (the "s"members having beentruncated at 60 Mb), butthe "d" series is absentin the calculations.Instead, a dip accompanieseach "s" member.

E. R. Brown, S. L. Carter,and H. P. Kelly, Phys.Rev. A 21, 1237 (1980).

801-

60k-4d155d

40 -

201-

NE0

0

b*1'

iiC I I I

(b)

401-

201-

4d 6s

K)14.5

-

1 L

'I

a

I

T

13.0

220

g. UV-laser Photodissociation of Molecular Ions (R. E. Kutina,A. K. Edwards, and J. Berkowitz)

The study of the interaction of electromagnetic radiation with

molecular ions represents an exciting challenge for the future, both in

terms of spectroscopy and of dynamics. One channel that is convenient for

experimental study occurs when the molecular ion dissociates as a

consequence of the interaction, yielding-a product which is easily

distinguishable from the target. In the present study, the primary ion is

produced by electron impact, mass-selected by a quadrupole mass

spectrometer, and crossed by pulsed exeimer-laser radiation. The fragment

ion is selected by a magnetic mass spectrometer. The precise momentum in

the laboratory frame can be related to kinetic energy release following

photodissocie.tion in the center of mass frame. A time-of-flight velocity

measurement provides equivalent information. An important feature of the

current experiments is the use of a UV laser (hv = 6.4 eV), whic i provides

sufficient energy to dissociate most molecular ions, whereas earlier

studies were largely limited to hV~ 2-3 eV and a correspondingly small set

of molecular ions.

We have examined the photodissociation of H2, HD+, D , D20+, OD+

ND3 and ND2 , all of which should have exothermic channels with hV - 6.4

eV. In this brief report, we can only summarize several striking

conclusions. Neither of the anticipated products (ND+ and D+) from ND2 is

observed. By contrast, both ND2 and ND+ fragments are detected from ND3 ,

although the latter process is endothermic for cold ND4. The dissociation

processes of OD+ to 0+ + D or D+ + 0 are almost isoergic, if all products

are in their ground states. We observe only 0+. It is not clear at this

time which upper state is responsible for the dissociation. Clearly, our

preliminary results are demonstrating that details of the potential energy

curves well beyond simple energetics will be necessary to interpret these

observations.

221

VIII. HIGH-RESOLUTION LASER-rf SPECTROSCOPY WITH ATOMIC AND MOLECULAR BEAMS

Introduction

The atomic-beam laser-rf double-resonance technique, devised in

1975-1976, provides a way for making extremely precise measurements of energysplittings in atomic or molecular systems. It has been used extensively since

then for the systematic investigation of the hyperfine structure (hfs) ofmetastable states of neutral atoms, and much of the key work has been done atArgonne. Except for a single feasibility study, however, no effort had been

made to use the powerful new technique for the study of challenging molecularstructure problems. In 1979 we selected the alkaline-earth monohalide

radicals for a comprehensive study with this method and in the 3 years since

then great progress has been made. The vibrational, rotational, and isotopic

dependence of many of the spin-rotational and hfs "constants" have beenmeasured to high precision for the calcium monohalide series, clearly

displaying a systematic, monotonic dependence on halide atomic number. For anumber of the parameters measured, no previous information was available for

any molecule of the class. New methods were devised to extend themeasurements to excited states, and the work has stimulated theoretical abinitio calculations to understand these "single-electron-outside-closed-

shells" molecular radicals. In the coming year, a major effort will be made

to undertake measurements of the electric dipole moments of these molecules.Such information, because of the very direct nature of its dependence on theelectronic wave functions, should be particularly valuable for a theoretical

understanding of the electronic states.

a. Hyperfine Structure of the Excited A 2n State of CaF

(W. J. Childs, David R. Cok, and L. S. Goodman)

The hfs spiittings of the A 2n excited state of CaF were found in

our early publications (1979-1980) to be too small to be measured with the

techniques then available. Our shift in 1981-1982 to digital data acquisition

and installation of a much more stable interferometer system for incremental

frequency measurement made observations of such small splittings (1--4 MHz) in

excited states possible, though still difficult. Measurements were carried

out both for the 2n3/2 and 2n1/ 2 states, and a definite J dependence was

observed. In addition, observations over a wide range of values of the

rotational quantum number N show a clear N-dependence. The theoretical

analysis is not yet complete.

Figure VIII-1 shows laser fluorescence spectra for the A211 / 2

X2E1/2 (at left) and A213/2 - X2E1/2 (at right) transitions in CaF. The

slight difference in the splitting of the P component shows that the A-state

hfs is J-dependent.

INCREMENTAL LASER

300 150 0

V2 j

I a

0 0 0

LASER WAVELENGTH(AT X6061.80)

FREQUENCY (MHz)

450 300 IOI

u

zuJzLU(9ZLU

LU

0:D-JLl.

Fig. VIII-l. Laser-induced fluorescence associated with the A 111/2 ++ X E1 /2 (left) and

A2 13/2 ++ X21/ 2 (right) transitions in CaF. The extremely small size of the hyperfine structure in

the excited A-state follows from the fact that the two spectra are nearly the same. A slight

difference in the splitting of the P transition gives evidence that they are not identical, however.

0

0~* V2v2

0o 2() 212

LASR AVLEGT

AT X635.50

223

b. The Hyperfine Structure of Alkaline-Earth Monohalide Radicals:New Methods and New Results, 1980-1982 (W. J. Childs)

A review paper summarizing- the present sta-: of our knowledge of the

spin-rotation and hyperfine interactions in the alkaline-earth monohalide

radicals was written and accepted for publication in Comments on Atomic and

Molecular Physics during the year. All work, from the first free-molecule

observations in 1980 up to the present is covered, and the enormous imprint of

the laser-rf double-resonance technique is made clear. The large body of

precise observations presented show systematic trends with respect to the

vibrational and rotational states and with respect to the halide atom (Z) or

isotope (A) chosen. New theoretical ag initi. work, stimulated by this body

of experimental results, is now underway jointly at Argornne and Northwestern

University.

c. New Line Classifications in Ho I Based on High-Precision hfsMeasurements of Low Levels (W. J. Childs, David R. Cok, andL. S. Goodman)

The hyperfine structure of all four members of the 4f'1 6s2 4I ground

term of Ho I was measured to high precision as a first step in a series of

several experiments to improve our understanding- of the 4f shell. The program

was stimulated by the new capability of carrying out multi-configuration

relativistic ab initio calculations in the rare-earth region. The possibility

of achieving a significantly better understanding of the different

contributions of relativity and configuration interaction to the hfs is now

real, and is of very special interest in the rare earth region because of the

collapse of the 4f shell near Z - 56. The Ho work also succeeded in

identifying- several very strong- previously unclassified "mystery" lines in the

Ho I optical spectrum. In addition, the study confirmed the finding- of other

recent work that the value of <r-3>4f associated with the electric-quadrupole

hfs is significantly smaller for configurations with a 4f11 core than fo'.

those with a 4f10 core. The origin of the effect is not yet understood, but

may be evidence of different Sternheimer shielding- for the two cases. A paper

on this work has been published in J. Opt. Soc. Amer. 73, 151 (1983).

224

'I. Modification of Apparatus for Electric-Dipole MomentMeasurement through the Stark Effect (L. S. Goodman)

Considerable effort has gone into preliminary design work for the

molecular Stark-effect-rf region to be introduced between the two laser-

molecular beam interaction regions of the double-resonance apparatus. An

extremely homogeneous d.c. electric field in which rf or microwave transitions

can be induced (1 MHz to 20 GHz) is required, and it must be thoroughly

shielded from the earth's magnetic field to prevent complications due to the

Zeeman effect. A satisfactory design concept has now been achieved and is

ready for detailing.

225

IX. BEAM-FOIL RESEARCH AND COLLISION DYNAMICS OF HEAVY IONS

Introduction

Our program consists of investigations of the structure anddynamics of atomic ions principally using photon detection techniques. The

experiments involve fast ion beams produced at either the Tandem-Linac

accelerator (30--500-MeV ion energy) or the Argonne Dynamitron accelerator

(0.5--4.5-MeV ion energy) or a low energy "test-bench" facility (0.02--0.12-

MeV ion energy). Laser excitation of the fast beams is anticipated in

future experiments to study atomic structure principally of low ionization

stages.

In 1982, the principal investigator, H. G. Berry, was in Europe

until the end of July; part of the time was spent at the Aim& Cotton

Laboratory, Orsay, France, learning laser techniques, and part of the time

at the University of Lund doing beam-foil spectroscopy with a small Tandem

accelerator.

The program at Argonne continued with a graduate student, JonHardis,* assisted by Professors A. E. Livingstont and L. J. Curtis* duringtheir frequent visits to Argonne. This work involved two atomic structureproblems in neon, plus a continuation of our study of electron channelplategeometries for More efficient data collection.

We have started our program of studies on the interactions of fastion beams with lasers. An argon-ion pump laser and a CW ring dye laser with

frequency-doubling capability have just been delivered. Initial experiments

on collinear laser-fast ion beam resonant excitation are under construction.

*Thesib student, University of Chicago, Chicago, IL.tUnivrsity of Notre Dame, Notre Dame, IN.*University of Toledo, Toledo, OH.

a. Lamb Shifts and Fine Structures of n = 2 in Helium-like Ions(H. G. Berry and J. E. Hardis*)

Following our successful calculations and experiments in silicon,

sulfur and chlorine of the ls2s3Sl - ls2p3P0,2 transition wavelengths, we

have continued this work in several directions:

(i) We are preparing a precision measurement in helium-like

titanium of the same transition. An initial run is scheduled at the Argonne

Tandem-Linac in early 1983. (See Fig. IX-1.)

(ii) A precision measurement in helium-like neon has been

completed at the Argonne Dynamitron. This experiment involved the use of an


226

48 9+ 216 MeV

300

250

200

400

WAVELENGTH (A)

Fig. IX-i. Preliminary spectrum of 216-MeV titanium. The two-electronTi XXI transition is noted.

Ti xxi 3S1 P 2

389.6 A

(00c0II II

C c

-C0 x_II x x

(0 c 0-II x

c -x IIx cx

x- x

(I)

zD0

150

0

C

II I(IC

X X

00

ii

100

50

0300 500 600

. . . . . . . . . . . . . . . . . . . .

227

8 MeV Ne2 + beam from the Dynamitron. The work should clarify some

discrepancies in recent measurements from other laboratories on these

transitions 1s2s3S1 - 1s2p3 P0, 2 and give a useful test of our two-electron

Lamb-shift calculations. The data are being analyzed.

(iii) We have improved our calculations of the total energies of

the two states 1s2s 3S and ls2p 3P for ions of low Z (Z < 10). We find

significant discrepancies in some previously published results. A

theoretical group at Oxford, England, (Grany et al.) have verified our

earlier calculations for these energies at higher Z.

b. Precision Wavel ngth Measurements in Helium (H. G. Berry,P. Juncar,* H. T. Duong-,* and R. Damaschini*)

In an experiment at Orsay, France, we have used saturated

absorption spectroscopy and a sigmameter to obtain the absolute wavelengths

of the 2p 3P0,1 ,2- 3d 3D1,2,3 transitions near 587.6 rn in 4 He I. Our

precision is about 8 parts in 109. By comparing- with recent two-photon

measurements of direct excitation from the 2s 3S1 level, we obtain values

for the wavelengths of the 2s 3S1 - 2p 3P0,1,2 transitions. Precise

calculations for these transitions are compared with experiment. In

particular, we have analyzed the QED and relativistic corrections.

*Laboratory of Aim& Cotton, Orsay, France.

c. Position-Sensitive Detector for UV Spectroscopy (J. E. Hardis*and H. G. Berry)

We continue to investigate designs of one-dimensional position-

sensitive detectors for the exit focus of our UV spectrometer. A

microchannel plate (MCP) serves as a front-end photon detector and signal

amplifier. Techniques for imaging the output electron signal of the MCP are

under study. Nonlinearities and drift in carbon-resistive-anode readouts

*Thesis student, University of Chicago, Chicago, IL.

228

limit theprecision of the effective spectral dispersion curve obtained.

Conductive wedges appear to hold promise, and computer modeling- is

underway. Application of digital VLSI technology and multi-anode techniques

are also under review.

d. High-spin States in Neon (J. E. Hardis,* A. E. Livingston,tL. J. Curtis,* and H. G. Berry)

Past experiments in this laboratory have identified the quartet

(1s2s2p 4 PO - 1s2p2 4 P) and quintet (1s2s2p2 5 P - 1s2p3 5S) transitions in

carbon, nitrogen, and oxygen. Higher beam energie- at the Dynamitron,

needed to excite the same doubly-excited states in heavier elements, were

not available. We have now a good source (2--3 uiA) of doubly-charged neon

for the Dynamitron accelerator. This effectively doubles the terminal

voltage for that projectile. The quartet spectral lines have been located,

and measurements of their wavelengths and lifetimes have been completed.

The quintet states have been identified and measurements of their

wavelengths and lifetimes are in progress.

*Thesis student, University of Chicago, Chicago, IL.

tUniversity of Notre Dame, Notre Dame, IN.

*University of Toledo, Toledo, OH.

e. Multicharged Ions.at the Dynamitron (J. E. Hardis,* R. Amrein,W. Ray and H. G. Berry)

In addition to upgrading the Dynamitron terminal voltage, we have

attempted to increase the energy of certain beams by producing multicharged

ions directly at the ion source. Tests with a Penning ion source have thus

far been disappointing. However, by careful adjustment of gas pressures and

mixtures (e.g., of Ne and H2), an rf ion source has given reasonable

quantities of well-focussed beams of Ne2+ and Arn+ with n - 2, 3, and 5.

Other rare gas ions should also be feasible. Addition of a crossed-field

analyzer at the source is expected to purify the higher charged beams.


229

f. Measurement of the Transition Probability of Singlet-TripletIntercombination Lines in Neon (L. J. Curtis*, J. E. Hardist,R. L. Brooks and A. E. Livingston*)

Using the same doubly-charged neon beam mentioned above, we have

measured the lifetimes of the neon 1s 2 2s3p 3P 0 , 1 , 2 states. The J - 1 state

has only about half the lifetime of the other two, and this difference is

attributed to the extra decay channel to the 1s22s2 IS state, accessible to

it alone. The smaller value for J = 1 is due to a J-allowed decay channel

to 2s2 10, and implies a transition probability of 4.3(6) x 108 sec-1 for

this intercombination line. These measurements extend similar measurement

of lighter elements done previously at lower energies (at Lund, Sweden).

This purely relativistic phenomenon is more pronounced in neon than in the

lighter elements.

*University of Toledo, Toledo, OH.

tThesis student, University of Chicago, Chicago, IL.

*University of Notre Dame, Notre Dame, IN.

g. Optical Measurements of Molecular-Ion Fragmentation (H. G. Berry,

L. Engstr5m,* S. Huldt,* and I. Martinson*)

In an experiment in Lund, Sweden, we observed the break-up of fast

CN+ ions in thin carbon foils. CH- was accelerated in a 3-MV Pelletron

Tandem accelerator and charge-exchanged to CN+ at the center gas stripper to

produce, typically, 100 nA of 5-MeV CN+ ions on target. Light yields from

several transitions in high ionization stages of C and N were observed to

vary as a function of carbon foil thickness. For very thin foils the

neighboring fragment ion is close enough to influence and enhance the

excited state production in these ions. The work is continuing both at

Argonne and at Lund. (See Fig. IX-2.)

*University of Lund, Sweden.

230

10

5 10 15 20 25 30f" 50FOIL THICKNESS (/p.g* cm 2 )

Fig. IX-2. Carbon-foil thickness dependence of carbon-ion and nitrogen-ion light yields for 5-MeV incident CN+ molecular ions.

0. C] Y385, 2p P - 3d D

XX N 628A 3s2S-4p2PXx

xx x x x x

x

I II I I I

CI[ 459, A2s2p3P-2s3d3D

0 S

I I I2 I

NIM 765A 2s S-2s2p Px

-xxx x x x X

SNIY 927A 2s2p 3P-2p2 3P

0 0

8

12

10

8

16

12

w

z

- 8

w 12

10

812

10

231

X. INTERACTIONS OF FAST ATOMIC AND MOLECULAR IONSWITH SOLID AND GASEOUS TARGETS

Introduction

Tightly collimated beams of molecular ions with energies variable inthe range 0.5--4.5 MeV are directed onto thin (''100 A) foil or gaseoustargets. The distributions in energy and angle are measured with highresolution (~0.005* and ~300 eV) for the resultant collisionally-induceddissociation fragments. The major aim of the work is a general study of theinteractions of fast ions with matter, but with emphasis on those aspectsunique to the use of molecular-ion projectiles. In addition, we are able tostudy of the structures of the incident molecular ions. These two differentaspects of the work are mutually interdependent. In order to derive structureinformation about a given molecular ion, one needs to know details about theway the dissociation fragments collectively interact with the target in whichthe dissociation occurs. Similarly, a knowledge of the structure of theincident molecular clusters is important in understanding the physics of theirinteractions with the target. We have therefore begun our work with carefulstudies involving beams of the simplest and relatively well understooddiatomic molecular ions (H2+, HeH+, etc.). Even with these, several new andinteresting- phenomena have been encountered (e.g., the interactions betweenthe molecular constituents and the polarization oscillations that they inducein a solid target,, the marked differences in dissociations induced in gases ascompared with those in foils, the anomalously high transmission of somemolecular ions through foils, and striking electron capture phenomena whencompared to atomic ions). As our understanding of these phenomena develops,we plan to go on to studies involving ever more complex projectile ions.

In the course of developing techniques for determining thestereochemical structures of molecular projectiles by coincident detection ofdissociation fragments, preliminary data have shown us the important problemswhich need to be addressed in order to obtain precise structuralinformation. Most prominently, these problems include the need for a moredetailed understanding of the physical processes involved in the interactionsof these fast molecular ions with solid targets and the formation of finalelectronic states. This year we concentrated our efforts on studying theformation of high Rydberg atoms when fast ions exit solids. These atoms werefound to emerge with high probability when fast molecular-ion beams dissociatein foils. Our work was aimed at understanding the processes which lead to theformation of these atoms. Also this year, we demonstrated that K-vacancyequilibration lengths for fast ions traversing solids are much longer thanpreviously anticipated. This was an important confirmation of our model forthe observed charge-state dependence of angular multiple-scattering widths forsuch ions.

Some of the highlights in 1982 included:

232

a. Contribution of Field-Ionized Rydberg Atoms to Convoy ElectronSpectra (D. S. Gemmell, Y.-Z. Gu, E. P. Kanter, D. Schneider,Z. Vager, and B. J. Zabransky)

A prominent feature observed in the energy spectrum of electrons

emitted in the forward direction from thin foils and gas targets under

bombardment by fast ions is a sharp cusp-shaped peak occurring at an energy

where the electron velocity matches the velocity of the emerging projectile

ions. For fast light ions, these "cusp" electrons were believed to originate

from the capture of target electrons into projectile-centered continuum

states. Intense experimental and theoretical efforts have been directed

towards understanding the measured cusps in terms of various theories of this

so-called electron-capture-to-the-continuum (ECC) model, as well as a

competing "wake-riding" model. To date, none of these various theoretical

treatments has had any success in explaining the full range of experimental

data now available from cusp-electron measurements. In pursuing our efforts

to explain some puzzling features of molecular-ion dissociation experiments

which had suggested the production of large numbers of high Rydberg atoms in

fast beams, we have also tried to determine the extent to which the presence

of significant numbers of such atoms could be affecting observations of cusp

electrons.

If electron capture can occur into continuum states lying just above

the ionization threshold of the projectile, there seems to be no a_ priori

reason why capture into bound states lying just below the ionization threshold

cannot also occur with comparable probability. The fate of Rydberg atoms

emerging from a target can be expected to depend sensitively, and in ways

difficult to predict, upon details of the experimental apparatus. Rydberg

atoms have long radiative lifetimes, but they can be ionized in quite modest

electric fields. Certainly the electric fields used in most electron

specrometers suffice to ionize a large fraction of Rydberg atoms entering the

spectrometer. Because it is customary in measurements of cusp electrons to

pass the projectiles emerging from the target through a spectrometer, it is

likely that field-ionizing Rydberg atoms will contribute electrons, traveling

with the beam velocity, to the secondary electron spectrum.

233

In our initial experiments, we incorporated a deflecting field

intermediate between the target and electron spectrometer. By jointly

sweeping the voltages on the deflecting plates, and the electron spectrometer,

we found that although electrons emerging from the target were eliminated as

anticipated by the deflecting field, there existed a sizable contribution of

beam-velocity electrons which originated after the deflecting field. Further

measurements with a +60 volt bias on the foil target shifted the cusp

electrons to lower energy and allowed a separation of the target "cusp" from

the field-ionizing Rydberg contribution.

We have further studied the systematics of this phenomenon with

various ion beams (both atomic and molecular), targets, beam energies, and

experimental geometries. Quite recently, we extended these measurements to

include highly energetic heavy-ion beams. Using the Argonne Tandem-Linac

heavy-ion accelerator, we studied the field ionization of high Rydberg- (n >

300) sulphur ions produced by beam-foil excitation of a 125-MeV sulphur

beam. That experiment conclusively demonstrated a very high yield of such

atoms as had been suspected from previous studies of the delayed x-ray

emission of these fast heavy ions.

These measurements, demonstrating- the large yield of Rydberg atoms

formed in excited fast ion beams, have far-reaching consequences in several

areas of atomic collision physics. Most importantly, many measurements of

charge-state yields and charge-changing cross sections must be reinvestigated

in the light of this discovery.

b. Microwave Field Ionization of Fast Rydberg Atoms (P. Arcuni,*D. S. Gemmell, E. P. Kanter, P. M. Koch,t D. R. Mariani,tD. Schneider, W. van de Water,t and B. J. Zabransky)

In an attempt to determine the quantum-state populations for beam-

foil excited high Rydberg atoms, we have collaborated with a group from Yale

University in studying the microwave ionization of such atoms. WOE used a


tYale University, New Haven, Connecticut.

234

750-keV H++80 volts target bias

Fig. X-1. A joint distribution of 00 electrons showing energy spectra forvarious levels of microwave power (watts). The lower-energy peak,unaffected by microwave power, is caused by convoy electrons. Thehigher-energy peak, which grows with power, is produced by field-Lo&ization of Rydberg atoms in the microwave cavity. At lower power,there is an additional contribution from atoms ionizing in thespectrometer field (170 v/cm).

235

9.91-GHz microwave cavity to ionize Rydberg atoms after production in a thin

carbon foil, but before entering the electron spectrometer field used to

energy-analyze the resulting electrons. Because of its high frequency, the

variable microwave electric field had only a negligible effect on the energy

spectrum of electrons originating prior to the cavity. By applying a bias

voltage to the foil target, we were able to separate clearly those electrons

produced at the target from those created in the cavity. An additional

contribution was observed from field ionization in the spectrometer field when

the microwave field was reduced below the magnitude of that field. (See

Fig. X-1.)

This experimental geometry separates the ionizing field from the

analyzing field, allowing us to vary the former to much higher values than we

had been able to achieve before. With a microwave power of 18.4 watts, we

achieved a maximum electric field of about 2.8 kV/cm which would ionize

hydrogen atoms as low as n = 24. Analysis of the data so far seems to

indicate that the n population is consistent with a simple OBK-type last-layer

capture process. It is hoped that a better understanding of the microwave

ionization process will yield more detailed information about the distribution

of kinetic energy of the electrons that we observe.

c. Coherent Stark States in Foil-Excited Fast Rydberg Atoms(D. S. Gemmell, E. P. Kanter, D. Schneider, and Z. Vager)

In a further effort to determine the quantum-state population of

foil-excited fast Rydberg atoms, we studied the field ionization of these

atoms in a variety of field geometries. One finding is that transverse

electric fields are more effective in ionizing such atoms than are

longitudinal fields. This is a strong indication of high alignment in the

excitation and suggests an electron density in these states which is oblate

with respect to the bean direction. A very surprising finding was the

observation of oscillations in the ionization yield when a longitudinal

electric field, starting at the target, is varied in magnitude. (See Fig. X-

2.) These oscillations are regularly spaced, with a period that varies with

the beam energy. We have demonstrated that these observations imply coherent

excitation of a few Stark levels near the unshifted center of the Stark

236

FIELD PERIOD (V/cm)

8 2 10 5 2800C-f -.

6 0.75-MeV H+ (a) (d) 0.75-MeV4 F 0.8 V/cm 0.8- H .

2000 -0.4

-20Ot

8000-6 1.5-MeV H+ (b) 2. - I.5-MeV ~4 AF= t 1.2V/cm 1.6- H

200 1.2

0.8400 VVV10.4-

8006 3.0-MeV H+ (C)_ 16- (f) 3-MeV

AF= 3.OV/cm 12 H -

8--2 4-40-

-80 -40 0 40 80 0 0.2 0.4 0.6 ..LONGITUDINAL FIELD (V/cm) FIELD FREQUENCY (V/cm)

Fig. X-2. A comparison of differential yield curves as a function oflongitudinal field for three different proton bombarding energies,(a) 0.75 MeV, (b) 1.5 MeV, and (c) 3 MeV, in the region between 100 V/cm.The square-wave fields, AF, are shown in each. The Fourier powerspectrum for each energy is shown in (d), (e), and (f), respectively.The Fourier spectra are computed from the full range of data measuredfor each energy.

237

manifold. The observed modulations are extremely sensitive to the amplitudes

of the coherently excited states. This phenomenon offers a new and

potentially powerful technique for studying excitation mechanisms that produce

high Rydberg- states of fast projectiles as they exit solids.

d. Equilibration Lengths of K-Vacancy Production in Solids(E. P. Kanter, D. Schneider, and B. J. Zabransky)

Measurements on the angular distributions of fast ions traversing

foils have shown a pronounced dependence of the multiple-scattering widths

upon the charge state of the emerging- ions. We have successfully explained

these results in terms of the large scattering angles achieved by those ions

that bear K vacancies. A quantitative model has been developed which

demonstrates how the "memory" of K-vacancy producing collisions gives rise to

large multiple-scattering widths in spite of apparent charge-state

equilibration. The K-shell capture and loss cross sections are an important

input to this model. Because these cross sections are largely unknown, we

have conducted a series of experiments to determine the K-shell charge-

exchange equilibration lengths for fast ions in foils. By measuring the yield

of KLL Auger electrons from 0.4- and 2.7-MeV W+ ions exiting solid carbon

targets, we have demonstrated that indeed the K-equilibration lengths are

longer than had been previously assumed, confirming our model of the multiple-

scattering- data.

e. Analysis of Molecular-Ion Stopping Power Measurements(D. S. Gemmell, E. Johnson,* E. P. Kanter, and M. F. Steuer)

Following the discovery in 1974 of the influence of cluster effects

upon the slowing- down of ions in solids, there have been several experimental

and theoretical investigations of this phenomenon. In general, the cluster

stopping powers for light projectiles such as H2+ are fairly well described on

the basis of wake models derived from Lindhard's dielectric function. The

situation for heavy clusters, however, appears to be more complex.

*Graduate student, Oxford University, England.

238

We have measured the stopping power ratio of N+ fragments from equal

velocity beams of N+ and N2 +. In contrast with the earlier work on light

ions, we were able to select molecular N+ fragment pairs that were

"longitudinally" aligned to the beam direction upon exiting the foil. This

orientational selectivity greatly simplifies the analysis.

Surprisingly, the results show that, contrary to the light ion data,

the stopping power of heavy molecular clusters is diminished relative to of

the corresponding monatomic projectiles. This implies that most of the

induced negative polarization charge must lie between the separating fragment

ions.

An intense effuzc to explain these data has yielded only limited

success. We have learned that it is vital to use a non linear wake model for

such heavy diatomic ions. To avoid the complexities of a proper quantum-

mechanical treatment we have employed a semiclassical calculation of free-

electron scattering- by two screened ionic cores to compute the stopping forces

as the ions traverse the solid. This method has had success in describing our

highest energy (3-MeV) stopping data, however, several problems limit the

applicability of this approach.

239

XI. THEORETICAL ATOMIC PHYSICS

Introduction

Our studies on the effects of relativity and electron correlationsin atomic processes consist of five major parts, three of which involve casestudies of atomic processes in the discrete, autoionization and continuumspectra, and two of which deal with the development of new techniques foratomic calculations.

(1) Rydberg Series Interactions in Ar, Kr and Xe Isc electronicSequences. Recent experiments on the absorption spectrum of Ba in theBeutler-Fano resonance region have opened up possibilities for studying-systematic trends of autoionization and Rydberg- series interactions alongisoelectronic sequences. In particular, the observed Ba++ spectrum is verydifferent from that of neutral Xe, showing- rapid changes in resonance profileswith increasing- nuclear charge. Theoretical spectra for Xe-like ions havebeen obtained with relativistic random-phase approximation (RRPA)calculations, and they are in very good agreement with experiment.Eigenchannel analysis of these spectra has revealed important information onthe influence of increasing nuclear charge on Rydberg- series interactions, andon the intimate relationship between electron correlation, term dependence andautoionization. A model is proposed to explain the system trend of resonanceprofiles in terms of the competition between atomic central potentials andelectron correlation effects along isoelectronic sequences. We shall makesimilar studies of the theoretical spectra for Ar- and Kr-like ions in theresonance region. Since the central potentials of these ions are differentfrom those of Xe-like ions, these studies can provide further tests of theproposed model.

The spectrum of Ba++ in the region of 5p+ns, nd discrete excitationsis also available experimentally. There are large variations in theintensities of absorption lines along Rydberg- series, reflecting strongchannel interaction effects. We shall employ the RRPA to provide ab initiodata for an eigenchannel analysis of the discrete spectrum of Ba+. Thisshould give important insights into the effect of Rydberg- series interactionson the observed line intensities.

(2) 4f Orbital Collapse for Pd-Like Ions. Because of thecompetition between the atomic central potential and the centrifugal barrier,the effective potential of f orbitals consists of an inner and an outer wellseparated by a potential barrier. For low Z ions, the 4f orbital resides inthe outer well and stays away from the atomic core. For Z > 58, it suddenlycollapses into the core region when the inner well is deep enough to support abound state. This sudden decrease in energy and size of the 4f orbital leadsto the filling of the 4f shell and the formation of the rare earths, and has aprofound influence on the spectra of these elements. Our recent study on theabsorption spectra of Xe-like ions in the region of 4d+nf, Cf excitationsshowed that orbital collapse is basically a shape resonance effect arisingfrom the interaction between the eigenstates of the inner well with those ofthe outer well. In particular, the observed Ba+ spectrum cqn be explained interms of the partial collapse of the 4f orbital in the 4d+f P channel. Weshall carry out further tests of our model of orbital collapse by studying- the

240

absorption spectra of Pd-like ions with a combination of the relativisticrandom-phase approximation and the term-dependent Hartree-Fock techniques. Asneutral Pd (Z=46) is further away from the region where orbital col p e takesplace, and as Pd has a rather simple ground-state configuration (rd S), weshould be able to make detailed studies of the spectra of Pd-like ions and togain better understanding of the collapse phenomenon along isoelectronicsequences.

(3) Hyperfine Structures of Rare Earth Elements. Importantinformation on the dynamics of many-electron correlation effects andrelativity can be obtained from atomic hyperfine structure studies.Traditionally, diagrammatic many-body perturbation theories are used toaccount for electron correlations and Dirac-Fock techniques are used to studyrelativistic effects on hyperfine structures. We shall attempt to study thecombined effect of electron correlations and relativity from amulticonfiguration Dirac-Fock (MCDF) point of view.

Our initial goal is to provide ab initio radial matrix elementswhich can be compared with experimental measurements. We shall study thehyperfine structures of rare earth element such as Ho Z = 7) and Er (Z =68) with ground state configurations of 4f 6s2 and 4f 2 6s , respectively.The chemical properties of the rare earths are determined mainly by the 4forbital which is known to go through a sudden decrease in energy and size (theso called "collapse" of the 4f orbital) at the beginning of this group ofelements. Atomic hyperfine structures of these elements can provide importantinformation on the properties of the collapsed 4f orbitals.

(4) Relativistic Phase Amplitude Method. The phase amplitudemethod describes the asymptotic behavior of continuum wave functions in termsof a relationship between the phase and the amplitude functions. Theamplitude function is in turn determined by a nonlinear equation derived fromthe Schridinger equation. This method is an important technique indetermining phase shifts and normalization factors of continuum wavefunctions, and in computing relevant matrix elements. It is also closelyrelated to many-body techniques such as the R-matrix theory and the closed-coupling method in atomic scattering calculations. We shall generalize thismethod to include four-component relativistic continuum wave functions. Thisis a first step towards a relativistic distorted wave Born approximationcalculation, which is useful, for example, for electron-impact-excitationcalculations involving highly stripped ions, and for inner-shell Augertransition studies.

(5) Multiconfiguration Relativistic Random-Phase Approximation.Starting from the time-dependent variational principle and amulticonfiguration Dirac-Fock ground state, we have obtained a set ofgeneralized RRPA equations which reduce to the usual RRPA equations when thereis only one configuration in the ground state. We are applying this newtechnique to low-energy photoionization studies, and eventually toautoionization studies in conjunction with the multichannel quantum defecttechnique. Our initial goal is to study the photoionization spectrum of Ba,where the usual RRPA technique is not quite capable of explaining the observedspectrum.

241

a. Transitions Between Quartet States of Three-Electron Ions(K. T. Cheng and H. G. Berry)

Transitions between the qua:tet states of (ls2snt) for nt = 4d, 4f,

5f and 5g are studied using a multiconfiguration Dirac-Fock (MCDF)

technique. These are satellite lines of the strong (ls2s2p)4P - (ls2s)4 P

transitions and are observed in the beam-foil spectrum of C3+. We found that

the coupling of the outer nL electrons with the (ls2s)3S and the (1s2p)3P

cores is weak, and that there are large deviations from the LS-coupling scheme

even for light ions such as C3+.

b. Influence of Increasing Nuclear Charge on the Rydberg Spectra ofXe, Cs' and Ba" (W. T. Hill III,* K. T. Cheng, W. R. Johnson,tT. B. Lucatorto,* T. J. Mcllrath,* and J. Sugar*)

The spectra of Xe, Cs+ and Ba++ in the region of Beutler-Fano

autoionization resonances are studied with a combined theoretical-experimental

effort. Theoretical resonance profiles are obtained from a relativistic

random-phase appv-ximation (RRPA) calculation. Systematic trends in the

resonance profiles are analyzed with the Multichannel Quantum Defect Theory

(MQDT). Our study demonstrates the intimate connection between electron-

electron correlation, term dependence and autoionization and underscore the

power of MQDT in analyzing complex spectra.

*National Bureau of Standards, Washington, DC.

tUniversity of Notre Dame, Notre Dame, Indiana.

*University of Maryland, College Park, Maryland.

c. Collapse of the 4f Orbital for Xe-Like Ions (K. T. Cheng andC. Froese Fischer*)

The effect of 4f orbital collapse on the spectra of Xe-like ions in

the region of 4d+nf, Ef excitations is studied using a term-dependent Hartree-

*Vanderbilt University, Nashville, Tennessee.

242

Fock technique. We found that the collapse phenomenon is basically a shape

resonance effect and that it is strongly term dependent. Also, the spectra of

Xe-like ions are determined mainly by the collapse of the 4f orbital in the

4d+f 1P channel. In particular, partial collapse of the 4f orbital is

responsible for the appearance of strong resonance lines in the observed Ba++

spectrum, thereby resolving the controversy regarding the interpretation of

this spectrum.

d. Photoionization of the Inner 4d Shells for Xe-Like Ions(K. T. Cheng and W. R. Johnson*)

Photoionization of the inner 4d shells for Xe, Cs+, Ba++ and La3+ is

studied using the relativistic random-phase approximation. Total cross

sections, partial cross-section branching ratios and angular distribution

asymmetry parameters are calculated, and their systematic trends along the

isoelectronic sequence are studied. Important dynamic effects of electron

correlations are obtained from an eigenchannel analysis. We, found that there

are shape resonances in the effective potential for f electrons, and that the

collapse of the 4f orbital along the isoelectronic sequence is closely related

to changes in f orbitals in passing through these resonances.

*University of Notre Dame, Notre Dame, Indiana.

e. Energy Level Scheme and Transition Probabilities of C R-Like Ions(K.-N. Huang,* Y.-K. Kim,* K. T. Cheng and J. P. Desclauxt)

The multiconfiguration Dirac-Fock technique is used to calculate

thirty-one low-lying levels of Ce-like ions. Breit interaction and Lamb shift

contributions are calculated perturbatively as corrections to the Dirac-

Fock energies. Probabilities for the El, Ml and E2 transitions connecting

excited levels with the ground levels are presented. These data are useful in

astrophysics and in controlled fusion research.

*Radiological and Environmental Research Division, ANL.

tCentre d'Etudes Nucleaires de Grenoble, Grenoble, France.

243

XII. ELECTRON SPECTROSCOPY WITH FAST ATOMIC AND MOLECULAR-ION BEAMS

Introduction

The study of inner-shell ionization phenomena arising in energetic

ion-atom collisions has been a field of experimental and theoretical interest

for many years. The experimental techniques of high-resolution electron andx-ray spectroscopy coupled with the availability of intense well-collimated,highly-monoenergetic beams of a great variety of atomic and molecular ionic

species at MeV energies, have opened many new avenues of research into inner-shell ionization phenomena. Although most of the early experiments were

performed under single-collision conditions (dilute gas targets), it has

recently been demonstrated that a wealth of valuable additional information

can be obtained when solid targets (thin foils) are employed. For studies

involving low-Z atoms (Z < 20), the spectroscopy of Auger electrons isespecially favored because of the low fluorescence yields.

The emission of Auger electrons following the dissociation of gas-and foil-excited fast (MeV) molecular-ion beams is investigated by measuring

single-electron spectra with high resolution. The spectra from ionic

fragments produced using molecular-ion beams are compared with spectra

produced using monatomic ion beams of the same velocity.

High-resolution Auger electron spectroscopy on target and projectile

species permits the study of excitation and transition probabilities fordifferent projectiles. In the case of He, for example, autoionizing stateshave been shown to interfere with continuum states. The interference pattern,

observed from the shapes of the lines observed in the electron spectrum,depends strongly on the electron observation angle and on the projectile

velocity, and charge state. From angle-dependent high-resolution measurements

it is possible to deduce the phase shift between the transition amplitudes forthe resonant (autoionization) and non-resonant (direct ionization)processes. If, in addition to the ion-beam excitation, a laser is used forselective excitation or for the "pumping" of excited states in the projectileor target atom, it should permit spectroscopy oa "exotic" states that can onlybe produced in violent ion-atom collisions. The advent of intense tunablelaser light sources has now made such experiments possible, e.g., the laser

could prepopulate specific outer-shell target states which subsequentlyinteract with a fast ion beam, producing inner-shell vacancies. This two-step

excitation process may enhance the creation of those short-lived autoionizingand Auger states that are not efficiently former in ion-atom collisionprocesses without lasers.

a. Investigation of Rydberg States Formed in Foil-Excited Fast Ion Beams(D. S. Gemmell, E. P. Kanter, D. Schneider, Z. Vager, and B. J. Zabransky)

We have extended our investigation of the formation of bound states

with high principal quantum numbers (Rydberg states) in a variety of fast,

foil-excited ion beams. Different field arrangements including microwave

244

fields have been applied to study the effect of field ionization of these

states. The yields of electrons produced via field ionization in the analyzer

were measured for a variety of atomic and molecular-ion beams. In the case of

125-MeV s14+ we have measured the absolute yield (for n z, 250) to be

~10-5/projectile. This value is consistent with recent findings of a group in

Munich who studied delayed K x-ray emission.

From our measurements it is clear that the neglect of the influence

of field-ionized Rydberg atoms in previous studies of convoy electrons may

have led to conflicting results when experiment and theory have been

compared. We also found that the contribution of electrons due to capture

into Rydberg states increases if molecular ions are used rather than atomic.

The higher probability for forming Rydberg states in the molecular case might

also account for unusual effects seen in the energy and angular distribution

of fragment ions following the dissociation of fast molecular ions in foil

targets.

The initial work has been followed by experiments in which the

ionizing field and the analyzing field are separate and can be varied

independently. For this purpose a microwave field was applied to the beam

prior to its entrance into the spectrometer. The microwave cavity was

designed so that the electrons emitted from the target could pass through the

high-frequency field with minimal disturbance. A large increase in the yield

of electrons due to field ionization was observed with increasing microwave

power. This demonstrated very impressively the high probability for forming

Rydberg states in fast ion beams penetrating foil targets. The maximum power

that could be applied to the cavity was 8 W corresponding to a maximum

longitudinal field of 2.4 kV/cm. This field is capable of ionizing hydrogenic

Rydberg states down to about n n 21.

To test the effect of field ionization in further detail, a

longitudinal electrostatic field was applied. The stripping field was

followed by a weak transverse field which enabled us to deflect target

electrons out of the spectrometer viewing region. Field ionization of the ion

beam could then be performed before the beam entered the analyzer field. By

using a digital lock-in technique (a small oscillating field was superimposed

on the longitudinal field) the differences in the ionization rates in the

245

spectrometer field were monitored. It was possible to resolve some

oscillatory structure in the yield curves. A transverse magnetic field also

allowed comparison of the dependence of the field ionization rate on the

direction of the field. It was found that transverse fields are much more

effective in field ionization than are the longitudinal fields. This is a

strong indication of high alignment in the excitation, suggesting an oblate

electron density in these Rydberg states with respect to the beam direction.

b. Inner-Shell Vacancy Fractions in Foil-Excited Ion Beams(P. J. Cooney, E. P. Kanter, D. Schneider, and B. J. Zabransky)

K-shell fractions for 2.7- and 0.4-MeV nitrogen ions exiting thin

carbon foils were measured as a function of foil thickness. The vacancy

fractions per projectile ion were deduced from measuring the yields of K-Auger

electrons emitted by the foil-excited nitrogen ions. It was found that the

vacancy fractions for these ions reach equilibrium only for foils thicker than

~'20 pg/cm2. The variation of the vacancy fractions in foils with thicknesses

below 20 hg/cm2 is a strong function of the projectile energy (Fig. XII-1). A

similar experiment was performed at the Argonne tandem accelerator with 45-MeV

F5+ ions. The results were found to be consistent with those for the nitrogen

case. Vacancy production cross sections derived from experiments with such

thin targets should be reconsidered in light of this finding.

c. Laser-Stimulated Ar L-Shell Excitation in Slow Ion-Atom Collisions

We have studied Ar L-shell excitation in slow heavy ion-atom

collisions for a large variety of collision systems. These studies have

confirmed that inner-shell vacancy production in systems where the ion

velocity is smaller than that of the relevant inner-shell orbital velocities

can be understood as electron promotion via coupliings between different

molecular orbitals (MO's) formed during the collision process. We plan to

perform experiments where we investigate the influence of L-shell vacancies in

systems like N + Ar or Ar + Ar due to additional photon excitation and/or

ionization of the quasimolecule formed in slow heavy ion-atom collisions.

246

' I I ' I

_ 1.6 IT: * MMWel_ .6 - ...-- - - - - - - - - 1 -

0 I

z 'I-

o I.4

- -j--0.4 MeV

z -- X-- 2.7MeVI 1.2

1.0 I ' I0 20 40 60 80 100

TARGET THICKNESS (pg/cm2)

Fig. XIl-1. K-vacancy fractions for nitrogen projectiles leaving carbonfoils as a function of foil thickness. Data is shown for 0.4- and2.7-MeV emergent ions. The solid and dashed curves result from fitsto the experimental data with a functional form

YK(x) = a /v(1--x/o).

247

d. Simultaneous Laser- and Ion-Beam Excitation of a Na Vapor Target

We plan to investigate the L-shell autoiontzation spectra of Na and

Na+ and the Na K-shell Auger-electron spectrum with simultaneous laser- and

ion-beam excitation. One goal of this study is to investigate whether

simultaneous laser/ion beam excitation can improve spectroscopic accuracy and

resolution. In the experiment a laser is used to excite the Na vapor from the

ground state to the Na*(ep) 2 P 3 / 2 state. Then a He+ beam at MeV energies will

be used for the L-shell excitation of the Na. Depending on whether the laser

is in or out, the probability for the excitation (and deexcitation), of the

Na L-shell should be different and detectable from the corresponding line

intensity. The sodium K-shell Auger-spectrum will also be measured as a

function of projectile energy and species to study multiple ionization.

e. Further Investigations of the Formation of Rydberg States in FastIon Beams

The experimental results on the formation of Rydberg states in fast

ion beams have opened many new questions. We intend to explore the mechanisms

leading to the formation of these states as fast ions exit solids. The

spectroscopy of these sta -s will be pursued using specific field arrangements

and microwave and/or laser spectroscopy techniques.

f. Study of Li-and He-Autoionization as a Function of Projectile Velocityand Charge State

The helium autoionization spectrum will be studied as a function of

Li-projectile charge state, the electron observation angle and the projectile

velocity. The goal is to examine the interference between a resonant process

(autoionization) and nonresonant process (direct ionization) both leading to

the same final (ionic) state. This interference can be studied from an

analysis of the asymetric line profiles. By applying theoretical model

calculations we expect to obtain the phase shift between the two relevant

transition amplitudes and the ratio of the amplitudes. The study will

therefore provide a test of the theoretical descriptions.

248

The investigation of the Li-autoionization spectrum following the

excitation of MeV Li-ions in various targets should give insight into the

formation of the excited states of Li in such collisions. In particular the

formation of Li- is of interest since it is a candidate for further

investigation involving laser-spectroscopy.

g. Auger-Electron Production Following Ion Collisions in Solids

The investigation of Auger-electron production following light- and

heavy-ion bombardment of solids will be continued. Reliable absolute yield

measurements will be the first goal of these studies. It should be possible

to deduce escape lengths for selected Auger-electrons. The latter will

involve measurements under channeling conditions to control the emission depth

of the electrons.

249/)b5-

PUBLICATIONS FROM 1 APRIL 1982 THROUGH 31 MARCH 1983,AND STAFF-MEMBERS OF THE PHYSICS DIVISION

251

PUBLICATIONS FROM 1 APRIL 1982 THROUGH 31 MARCH 1983

The list of "journal articles and book chapters," is classified bytopic; the arrangement is approximately that followed in the Table ofContents of this Annual Review. The "reports at meetings" includeabstracts, summaries, and full texts in volumes of proceedings; they arelisted chronologically.

A. JOURNAL ARTICLES AND BOOK CHAPTERS

Isospin Effects in Pion Single-Charge-Exchange ReactionsD. Ashery, D. F. Geesaman, R. J. Holt, H. E. Jackson, J. R.Specht, K. E. Stephenson, R. E. Segel (Northwestern), P.Zupranski (Northwestern), H. W. Baer (LANL), J. D. Bowman(LANL), M. D. Cooper (LANL), M. Leitch (LANL), A. Erel (TelAviv. U.), R. Chefetz (Tel Aviv U.), J. Comuzzi (MIT), R. P.Redwine (MIT), and D. R. Tieger (Boston U.)

Phys. Rev. Lett. 50, 482, (1983)

Isospin Splitting of the Giant Dipole Resonance in 60NiT. J. Bowles, R. J. Holt, H. E. Jackson, R. D. McKeown, A. M.Nathan (U. Illinois), and J. R. Specht

Phys. Rev. Lett. 48, 986 (1982)

Erratum: Isovector Radiavie Decays and Second-Class Currents in Mass 8Nuclei [Phys. Rev. C 18, 1447 (1978)]

T. J. Bowles and G. T. GarveyPhys. Rev. C 26, 2336 (1982)

Measurement of the 7 Be(p,Y)8B Reaction Cross Section at Low EnergiesB. W. Filippone, A. J. Elwyn, C. N. Davids, and D. D. Koetke(Valparaiso U.)

Phys. Rev. Lett. 50, 412 (1983)

Demgstration of the Need for Meson Exchange Currents in the Beta Decayof N(O)

C. A. Gagliardi, G. T. Garvey, J. R. Wrobel, and S. J. Freedman(Stanford U.)

Phys. Rev. Lett. 48, 914 (1982)

Erratum: Beta-Alpha Angular Correlations in Mass 8 [Phys. Rev. C 22, 738(1980)]

R. D. McKeown, G. T. Garvey, and C. A. GagliardiPhys. Rev. C 26, 2336 (1982)

Observation of the (i~, nrn) and (i+,,ir+p) Reactions at 165 MeVE. Piasetsky (Tel Aviv U.), A. Altman (Tel Aviv U.), J.Lichtenstadt (Tel Aviv U.), A. I. Yavin (Tel Aviv U.), D.Ashery, W. Bertl (ETH, Zurich), L. Felawka (ETH, Zurich), H. K.Walter (ETH, Zurich), F. W. Schlepotz (U. Zurich), R. J. Powers(U. Zurich), R. G. Winter (U. Zurich and C. of Wm. and Mary),and J. v. d. Pluym (Vrije U., Amsterdam)

Phys. Lett. 114B, 414 (1982)

252

Pion-Induced Nucleon Knockout Reactions on 160 and 180E. Piasetzky (Tel Aviv U.), A. Altman (Tel Aviv U.), J.Lichtenstadt (Tel Aviv U.), A. I. Yavin (Tel Aviv U.), D.Ashery, W. Bertl (ETH, Zurich), L. Felawka (ETH, Zurich), H. K.Walter (ETH, Zurich), F. W. Schlepitz (U. Zurich), R. J. Powers(U. Zurich), R. G. Winter (U. Zurich and C. of Wi. and Mary),and J. v. d. Pluym (Vrije U., Amsterdam)

Phys. Rev. C 26, 2702 (1982)

Study of the 3 9 ,41K(d, 3He) 38 ,40 Ar Reactions at 22.8 MeVC. M. Bhat (Bangalore U., India), M. Raja Rao (Bangalore U.),N. G. Puttaswamy (Bangalore U.), and J. L. Yntema

Nucl. Phys. A394, 109 (1983)

7Li(d,p)8Li Reaction Cross Section Near 0.78 MeVA. J. Elwyn, R. E. Holland, C. N. Davids, and W. Ray, Jr.

Phys. Rev. C 25, 2168 (1982)

Absolute Cross Section for 7Li(d,p)8Li and Solar Neutrino Capture RatesB. W. Filippone, A. J. Elwyn, W. Ray, Jr., and D. D. Koetke(Valparaiso U., Indiana)

Phys. Rev. C 25, 2174 (1982)

y Decay of States in 4 7 CrG. Hardie (Western Mich. U., Kalamazoo, MI), S. A. Gronemeyer,L. Meyer-Schitzmeister, and A. J. Elwyn

Phys. Rev. C 26, 456 (1982)

180Tag,m Production Cross Sections from the 1 80Hf(p,n) ReactionEric B. Norman, Timothy R. Renner, and Patrick J. Grant (U.Washington, Seattle, WA)

Phys. Rev. C 26, 435 (1982)

Prompt Compound Nuclear K x Rays in Fusion Reactions Induced by a HeavyProjectile

H. Ernst, W. Henning, C. N. Davids, W. S. Freeman, T. J.Humanic, M. Paul, S. J. Sanders, F. W. Prosser, Jr. (U.Kansas), and R. A. Racca (U. Kansas)

Phys. Lett 119B, 307 (1982)

Search for Transient Electric Field Gradients Acting on Fast-Moving Ionsin Solids

H. Ernst, W. Henning, T. J. Humanic, T. L. Knoo, Steven C.Pieper, and J. P. Schiffer

Phys. Rev. C 26, 2039 (1982)

Reactions to Resolved States and to Non-fusion Channels for 160 + 4 8 Caat Elab = 158.2 MeV

T. J. Humanic, H. Ernst, W. Henning, and B. ZeidmanPhys. Rev. C 26, 993 (1982)

253

Nuclear Radiation

Dennis G. KovarMcGraw-Hill Encyclopedia of Science and Technology, 5thedition, ed. by S. P. Parker (McGraw-Hill, NY, 1982), pp.320-321

Nuclear Reaction

Dennis G. Kovar

McGraw-Hill Encyclopedia of Science and Technology, 5thedition, ed. by S. P. Parker (McGraw-Hill, NY, 1982), pp.322-326

Inelastic Scattering and One-Neutron-Transfer Reactions of 180 + 40CaK. E. Rehm, W. Henning, J. R. Erskine, and D. G. Kovar

Phys. Rev. C 26_, 1010 (1982)

Inelastic Scattering of 1 60 from 40,42,44,48CaK. E. Rehm, W. Henning, J. R. Erskine, D. G. Kovar, M. H.Macfarlane, S. C. Pieper, and M. Rhoades-Brown

Phys. Rev. C 25, 1915 (1982)

Strong Popy at n of Excited 0+ States in Even Zr Isotopes Observedwith the ( C, 0) Reaction

Wolfgang Mayer (Technische Universitg't Munchen, Garching, W.

Germany), D. Pereira (TUM, Germany), K. E. Rehm (TUM, Germany),H. J. Scheerer (TUM, Germany), H.J. K6rner (TUM, Germany), G.Korschinek (TUM, Germany), Waltraud Mayer (TUM, Germany), P.

Sperr (TUM, Germany), Steven C. Pieper, and R. D. LawsonPhys. Rev. C 26, 500 (1982)

High Spin States in 9 4Ru and 95Rh

A. Amusa (PHY/U. Ife) and R. D. LawsonZ. Phys. A 307, 333 (1982)

Relativistic Quantum Mechanics of Particles with Direct InteractionsF. Coester and W. N. Polyzou (MIT)

Phys. Rev. D 26, 1348 (1982)

Coherence, Mixing, and Interference Phenomena in Radiative J DecaysIsaac Cohen (Weizmann Inst., Israel), Nathan Isgur (U.Toronto), and Harry J. Lipkin

Phys. Rev. Lett. 48, 1074 (1982)

Isospin Dependence of Pion Absorption on 3 HeT.-S. H. Lee and K. Ohta (MIT, Cambridge)

Phys. Rev. Lett. 49, 1079 (1982)

Microscopic Study of the A-Nucleus Potential from a Many-BodyHamiltonian for Tr, N and A

T.-S. H. Lee and K. Ohta (MIT, Cambridge)Phys. Rev. C 25 3043 (1982)

254

Angular Momentum Paradoxes with Solenoids and MonopolesHarry J. Lipkin and Murray Peshkin

Phys. Lett. 118B, 385 (1982)

Isotope Targets Prepared by Vapor DepositionG. E. Thomas

Nucl. Instrum. Methods 200, 27 (1982)

High Intensity Inverted Sputter SourceJ. L. Yntema and P. J. Billquist


Yrast (h 11/2)n Excitations in Proton-Rich N=82 NucleiH. Helppi (Purdue U.), Y. H. Chung (Purdue U.), P. J. Daly(Purdue U.), S. .R. Faber (Purude U.), A. Pakkanen (Purdue U.),I. Ahmad (CHM), P.Chowdhury, Z. W. Grabowski, T. L. Khoo, R. D.Lawson, and J. Blomqvist (Res. Inst. Phys., Stockholm)

Phys. Lett. 115B, 11 (1982)

Transitigfrom Collective to Aligned-Particle Configurations at HighSpin in Dy

A. Pakkanen (Purdue U.), Y. H. Chung (Purdue U.), P. J. Daly(Purdue U.), S. R. Faber (Purdue U.), H. Helppi (Purdue U.), J.Wilson (Purdue U.), P. Chowdhury, T. L. Khoo, I. Ahmad (CHM),J. Borggreen, Z. W. Grabowski, and D. C. Radford (Yale U.)

Phys. Rev. Lett. 48, 1530 (1982)

Search for Structure in the Fusion of 160 + 2 4MgR. A. Racca (U. of Kansas), F. W. Prosser (U. of Kansas), C. N.Davids, and D. G. Kovar

Phys. Rev. C 26, 2022 (1982)

Photoionization Mass Spectrometry of NH2OH: Heats of Formation of HNO+and NOH+

R. E. Kutina, G. L. Goodman and J. BerkowitzJ. Chem. Phys. 77, 1664-1676 (15 Aug. 1982)

Photoionization Mass Spegtrometr of CH3SH, CD34 H and CH3SD: Heats ofFormation of CH3S (CH2SH ), CH2S , CH2S and HCS

R. E. Kutina, A. K. Edwards, G. L. Goodman and J. BerkowitzJ. Chem. Phys. 77, 5508-5526 (1 Dec. 1982)

Hyperfine Structure of the X 2E Ground State of Ca35C1 and Ca 3 7 C1 byMolecular-Beam Laser-rf Double Resonance

W. J. Childs, David R. Cok, and L. S. GoodmanJ. Chem. Phys. 76, 3993-3998 (15 April 1982)

Hyperfine Structure of the A 2r State of Ca 3 5 C1W. J. Childs, David R. Cok, and L. S. Goodman

J. Opt. Soc. Am. 72, 717-719 (June 1982)

255

Vibrational, Rotational, and Isotopic Dependence of CaBr X 2E Spin-Rotational and hfs Parameters

W. J. Childs, David R. Cok, and L. S. GoodmanJ. Mol. Spectrosc. 95, 153-156 (1982)

New Line Classifications in Ho I Based on High-Precision Hyperfine-Structure Measurement of Low Levels

W. J. Childs, David R. Cok, and L. S. GoodmanJ. Opt. Soc. Am. 73, 151 (1983)

Doubly Excited States in Some Light AtomsH. Gordon Berry, Robert L. Brooks, Jonathan E. Hardis,and W. J. Ray

Nucl. Instrum. Methods 202, 73-77 (1982)

Comparisons Between Theory and Experiment in Two Electron SystemsH. G. Berry, R. DeSerir. and R. L. Brooks

Nucl. Instrum. and Methods 202, 95-101 (1982)

Beam-Foil SpectroscopyH. G. Berry and M. Hass (Weizman Inst., Rehovot, Israel)

Ann. Rev. Nucl. Part. Sci. 32, 1-34 (1982)

Hyperfine Structures of the nd 1 D(n = 3--8) States of 3He IRobert L. Brooks, Vincent F. Streif and H. Gordon Berry


Alignment and Orientation of the 3p 3 P He I Term After Tilted-FoilExcitation

R. L. Brooks, H. G. Berry and E. H. Pinnington (Univ. ofAlberta, Edmonton, Alberta, Canada)

Phys. Rev. A 25, 2545-2549 (1982)

Measurement of the Transition Probability of the 2s2 1S0 -2 s3 p 3P4Intercombination Line in Ne VII

J. E. Hardis, L. J. Curtis, P. S. Ramunujam, A. E. Livingston,and R. L. Brooks

Phys. Rev. A27, 257--261 (January 1983)

Spectroscopie et Mesures de Vies Moyennes de Niveaux de Nickel HautementIonise

C. Jacques (Universite Laval, Quebec, Canada), M. Druetta(Universite de Lyon, Villeurbanne, France), H. G. Berry and E.J. Knystautas (Universite Laval, Quebec, Canada)


Energies of Some Triplet Levels in 4He IP. Juncar (Lab. Aime Cotton, France), H. G. Berry, R.Damaschini (Lab. Aime Cotton), and H. T. Duong (Lab. AimeCotton)

J.Phys. B: At. Mol. Phys. 16, 381 (1983)

256

Collisional Effects in the Passage of Fast Molecular Ions Through ThinFoils

Donald S. GemmellNucl. Instrum. Methods 194, 255 (1982)

Ion-Source Dependence of the Distributions of Internuclear Separationsin 2-MeV HeH+ Beams

Elliot P. Kanter, Donald S. Gemmell, Itzhak Plesser, and ZeevVager


Diminished Stopping Power for Fast Nitrogen and Oxygen Diclusters inCarbon

Malcolm F. Steuer, Donald S. Gemmell, Elliot P. Kanter, EdwardA. Johnson, and Bruce J. Zabransky


Influence of Increasing Nuclear Charge on the Rydberg Spectra of Xe, Cs+and Ban: Correlation Term Dependence, and Autoionization

W. T. Hill III (NBS), K. T. Cheng, W. R. Johnson (U. of NotreDame), T. B. Lucatorto (NBS), T. J. Mcllrath (U. Maryland), andJ. Sugar (NBS)

Phys. Rev. Lett. 49, 1631 (1982).

Correlation and Relativistic Effects in Spin-Orbit SplittingsK.-N. Huang (RER), Y.-K. Kim (RER), K. T. Cheng, and J. P.Desclaux (Grenoble)

Phys. Rev. Lett 48, 1245 (1982).

Target--Thickness Dependence of K-Shell Vacancy Fractons in Foil-ExcitedIon Beams

D. Schneider, E. P. Kanter, and B. J. ZabranskyPhys. Rev. A 26, 3700-3701 (1982)

257

B. PUBLISHED REPORTS AT MEETINGS

Proceedings of the International School of Physics "Enrico Fermi", Varenna,Italy, 23 June-5 July 1980.

Brueckner-Bethe Calculations of Nuclear MatterB. D. Day

Course LXXIX ed. by A. Molinari (North-Holland,Amsterdam, 1981), pp. 1-71

Proceedings of the Netherlands Physical Society 1980 International SummerSchool on Nuclear Structure, Dronten, The Netherlands, 12-23 August 1980.

Nuclear Structure and Heavy-Ion ReactionsJohn P. Schiffer

Ed. by K. Abrahams, K. Allaart, and A. E. L. Dieperink(Plenum, NY, 1981), pp. 127-163

Proceedings of the Ninth World Conference of the International Nuclear

Target Development Society, Gatlinburg, Tennessee, 13-16 October 1980

Isotope Targets Prepared by Vapor DepositionG. E. Thomas

Ed. by E. H. Kobisk and H. L. Adair (North-Holland,1982), pp. 27-31 [Reprinted from Nucl. Instrum. Methods200, 27 (1982)]

Proceedings of the Sixth International Conference on Fast Ion BeamSpectroscopy, Laval, Quebec, Canada, 17-20 August 1981

Doubly Excited States in Some Light AtomsH. Gordon Berry, Robert L. Brooks, Jonathan E. Hardis,and W. J. Ray

Ed. by E. J. Knystautas and R. Drouin (North-Holland,1982) +Nucl. Instrum. Methods 202, 73 (1982)

Comparisons Between Theory and Experiment in Two Electron SystemsH. G. Berry, R. DeSerio, and R. L. Brooks

Ed. by E. J. Kynstautas and R. Drouin (North-Holland,

1982) +Nucl. Instrum. Methods 202, 95-101 (1982)

Hyperfine Structures of the nd 1 D(n = 3--8) States of 3 He IRobert L. Brooks, Vincent F. Streif, and H. Gordon Berry

Ed. by E. J. Kynstautas and R. Drouin (North-Holland,1982)+Nucl. Instrum. Methods 202, 113 (1982)

Spectroscopie et Mesures de Vies Moyennes de Niveaux de NickelHautement Ionise

C. Jacques (U. of Laval, Quebec), M. Druetta (U. of Lyon,France), H. G. Berry, and E. J. Knystautas (U. Laval)

Ed. by E. J. Kynstautas and R. Drouin (North-Holland,1982)+Nucl. Instrum. Methods 202, 45 (1982)

258

Proceedings of the 1981 Annual Meeting of the Optical Society of America,Kissimmee, Florida, 26-30 October 1981

Photoionization of Atoms and MoleculesJ. Berkowitz

J. Opt. Soc. Am. 71, 1579 (1981)

Proceedings of the U.S.-Japan Seminar on Charged-Particle PenetrationPhenomena, Honolulu, Hawaii, 25-29 January 1982

"Interactions of Fast Molecular Ions Traversing Thin Foils" - "TheContribution from Field-Ionized Rydberg Atoms in Measurements onConvoy Electrons"

Donald S. GemmellNational Technical Information Service, Springfield,Virginia, 1983), CONF-820131, pp. 222-255

Proceedings of the Conference on Lasers in Nuclear Physics, Oak Ridge,Tennessee, 21-23 April 1982

On-Line Laser Spectroscopy with a Cooled He-Jet Transport SystemDavid Lewis (Iowa State U.), Rollin Evans (Iowa State), CaryDavids, Miles Finn (U. Minnesota), George Greenlees(Minneosta), and Stanley Kaufman (Minnesota)

Ed. by C. E. Bemis, Jr. and H. K. Carter (HarwoodAcademic Publishers, NY, 1982), pp. 189-196

APS Meeting, Washington, D.C., 26-29 April 1982

Elastic Scattering and Reactions of 40Ca + 4 0 CXaR. R. Betts (CHM Div., ANL), I. Ahmad (CHM), B. B. Back(CHM), B. G. Glagola (CHM), W. Henning, S. Saini (CHM), andJ. L. Yntema

Bull. Am. Phys. Soc. 27, 474 (1982)

usionil 28n 2Seep-InelasticReaction Cross Sections for

H. Ernst, C. N. Davids, W. S. Freeman, W. Henning, T.Humanic, F. W. Prosser (U. Kansas), and R. Racca (Kansas)

Bull. Am. Phys. Soc. 27, 475 (1982)

Measurement of the Beta Decay.of 16N(0-, 120 keV): The Need for

Meson Exchange Currents and the Value of gC. A. Gagliardi, G. T. Garvey, S. J. freedman (Stanford), andJ. R. Wrobel

Bull. Am. Phys. Soc. 27, 492 (1982)

Fundamental Aspects of Nuclear Beta DecayG. T. Garvey

Bull. Am. Phys. Soc. 27, 463 (1982)

259

APS, Washington, D.C., 26-29 April 1982 (contd.)

Search for Transient Electric Field Gradients Acting on Fast-Moving Ions in Solids

T. J. Humanic, H. Ernst, W. Henning, T. L. Khoo, Steven C.Pieper, and J. P. Schiffer

Bull. Am. Phys. Soc. 27, 520 (1982)

T0F Mea urements of Evaporation Residues Produced in 160 + 12C and60 + 2 Mg at 4 S 9.4 MeV/A

T. Humanic, D. G. Kovar, R. Betts (CHM Div., ANL), P.Chowdhury, D. Henderson, R. V. F. Janssens, W. Khn, and K.Wolf (CHM)

Bull. Am. Phys. Soc. 27, 478 (1982)

A gular9 omentum Dependence of Neutron Spectra in the 250-MeVNi + Zr Reaction

W. Kuhn, I. Ahmad (CHM Div., ANL), P. Chowdhury, R. V. F.Janssens, T. L. Khoo, F. Haas (Mich. State U.), J. Kasagi(MSU), and R. M. Ronningen (MSU)

Bull. Am. Phys. Soc. 27, 475 (1982)

Energy Dependence of 2 4Mg + 2 4Mg Elastic Scattering and ReactionsS. Saini (CHM Div., ANL), R. R. Betts (CHM), I. Ahmad (CHM),B. B. Back (CHM), G. B. Glagola (CHM), J. L. Yntema, R. W.Zurmuhle (U. Penn.), and F. Haas (Mich. State U.)

Bull. Am. Phys. Soc. 27, 480 (1982)

Measurement of the 2 H(Y,n) 1 H Relative Cross Section at EY S 19 MeVK. Stephenson, R. E. Holland, R. J. Holt, H. E. Jackson, R.D. McKeown, and J. R. Specht

Bull. Am. Phys. Soc. 27, 570 (1982)

High Intensity Inverted Sputter SourceJ. L. Yntema and P. J. Billquist

Bull. Am. Phys. Soc. 27, 521 (1982)

30th Annual Conference on Mass Spectrometry and Allied Topics, Honolulu,Hawaii, 6-11 June 1982

Photoionization Mass Spectrometry of CH3SH, CD3SH and CH SD:Heats of Formation of CH3S(CH2 SH), CH2S , CH2S and HCS

R. E. Kutina, A. K. Edwards, G. L. Goodman, and J. BerkowitzProc. ed. by F. W. Lampe (American Soc. for MassSpectrometry, 1982), Abstracts, pp. 617-618

Phojoionization Mass Spectrometry of NH20H: Heats of Formation ofHNO and NOH

R. E. Kutina, G. L. Goodman, and J. BerkowitzProc. ed. by F. W. Lampe (American Soc. for Mass

Spectrometry, 1982), Abstracts, pp. 504-505

260

30th Annual Conference on Mass Spectrometry and Allied Topics, Honolulu,Hawaii, 6-11 June 1982 (contd.)

Photoelectron Spectra of Gas Phase Lanthanide TrihalidesB. M. Ruscic, G. L. Goodman, and J. Berkowitz

Proc. ed. by F. W. Lampe (American Soc. for MassSpectrometry, 1982), Abstracts, pp. 700-701

Proceedings of the 1982 INS International Symposium on Dynamics of NuclearCollective Motion--High Spin States and Transitional Nuclei, Tokyo, Japan,6-10 July 1982

Shell Structure at High Spin and the Influence on Nuclear ShapesT. L. Khoo, P. Chowdhury, I. Ahmad (CHM Div., ANL), J.Borggreen, H. Emling, D. Frekers, R. V. F. Janssens, A.Pakkanen (Purdue U.), Y. H. Chung (Purdue), P. J. Daly(Purdue), S. R. Faber (Purdue), Z. Grabowski (Purdue), H.Helppi (Purdue), M. Kortelahti (Purdue), and J. Wilson(Purdue)

Ed. by K. Ogawa and K. Tanabe (Inst. for Nucl. Study, U.of Tokyo, Japan, Sept. 1982), pp. 256-274

International Conference on X-Ray and Atomic Inner-Shell Physics, Eugene,Oregon, 23-27 August 1982

The Effect of Inner-Shell Vacancies on Multiple ScatteringDistributions of Heavy-Ion Beams Traversing Solids

E. P. KanterEd. by B. Crasemann (U. of Oregon, 1982) Program andAbstracts, Vol. 1, pp. 132-133

Equilibration Lengths for K-Shell Charge-Exchange Processes forFast Ions Traversing Foils - Evidence from Multiple-ScatteringDistributions and Auger-Yield Measurements

Elliot P. Kanter, Dieter Schneider, and Donald S. GemmellEd. by B. Crasemann (American Inst. of Physics, NY,1982) pp. 735-744+ Program and Abstracts (U. of Oregon, 1982), Vol 1, p.169

Auger-Electron Spectroscopy on Foil and Gas Excited Fast-Atomicand Molecular-Ion Beams

D. Schneider, E. P. Kanter, D. S. Gemmell, and B. J.

ZabranskyEd. by B. Crasemann (U. of Oregon, 1982)Program and Abstracts, Vol. 2, pp. 186-187

SNEAP '82 (Symposium of Northeastern Accelerator Personnel, Seattle,Washington, 6-8 Oct. 1982)

1982 SNEAP Tandem-Linac Accelerator ReportP. Den Hartog, R. Pardo, F. Munson, and C. Heath

Ed. by W. G. Weitkamp (Univ. of Washington, 1982), pp.166-168

261

SNEAP '82 (Symposium of Northeastern Accelerator Personnel, Seattle,Washington, 6-8 Oct. 1982) (contd.)

A Terminal Lens for an FN TandemP.K. Den Hartog, F. H. Munson, and C. E. Heath

Ed. by W. G. Weitkamp (Univ. of Washington, 1982), pp.84-91

Ion Source Development at ArgonneP.J. Billquist and J. L. Yntema

Ed.by W. G. Weitkamp (Univ. of Washington, 1982), pp.261-267

American Physical Society, Division of Nuclear Physics, Amherst,Massachusetts, 14-16 October 1982

Fusion of 6 4Ni Beams Incident on the Even Sn IsotopesW. S. Freeman, D. F. Geesaman, W. Henning, W. Kuhn, J. P.Schiffer, B. Zeidman, and F. W. Prosser (U. Kansas)

Bull. Am. Phys. Soc. 27, 707b (1982)

Measurement of the Ti Half-Life Via Tandem Accelerator MassSpectrometry

D. Frekers, W. Henning, W. Kutschera, K. E. Rehm, R. K.Smither, J. L. Yntema, and B. Stievano (INFN, Legnaro, Italy)

Bull. Am. Phys. Soc. 27, 712 (1982)

Fragmentation of High-Spin Particle-Hole States in 26MgD. F. Geesaman, B. Zeidman, C. Olmer (Indiana U.), A. D.Bacher (Ind. U.), G. T. Emery (Ind. U.), C. W. Glover (Ind.U.), H. Nann (Ind. U.), W. P. Jones (Ind. U.), S. Y. van derWerf (KVI, Groningen), R. E. Segel (Northwestern U.), and R.A. Lindgren (U. Mass., Amherst)

Bull. Am. Phys. Soc. 27, 697 (1982)

Electroproduction of HypernucleiT.-S. H. Lee and J. P. Schiffer

Bull. Am. Phys. Soc. 27, 719 (1982)

Mea grements of Transverse Electron Scattering Cross Sectionsin Mg

R. A. Lindgren (U. Mass., Amherst), M. A. Plum (U. Mass.), R.L. Huffman (U. Mass.), R. S. Hicks (U. Mass.), X. K. Maruyama(NBS, Wash., D.C.), A. D. Bacher (Ind. U.), C. Olmer (Ind.U.), D. F. Geesaman, and B. H. Wildenthal (Mich. State U.)

Bull. Am. Phys.Soc. 27, 697 (1982)

American Physical Society, New York, New York, 24-27 January 1983

Nuclear Physics with Several-GeV ElectronsGerald Garvey

Bull. Am. Phys. Soc. 28, 50 (1983)

262

American Physical Society, New York, New York, 24-27 January 1983 (contd.)

High Spin State in NucleiT. L. Khoo

Bull. An. Phys . Soc. 28, 50 (1983)

263f26+i

C. ANL PHYSICS DIVISION REPORTS

GeV C. W. Electron Microtron Design Reported. by H. E. Jackson

Argonne National Laboratory Topical ReportANL-82-22 (May 1982)

A National CW GeV Electron Microtron Laboratoryed. by H. E. Jackson

Argonne National Laboratory Topical ReportANL-82-83 (December 1982)

265

STAFF MEMBERS OF THE PHYSICS DIVISION

Listed below are the permanent staff of the Physics Division for the yearending 31 March 1983. The program heading indicates only the individual'scurrent primary activity.

EXPERIMENTAL NUCLEAR PHYSICS AND ACCELERATOR PHYSICS

Scientific Staff

Lowell M. Bollinger, Ph.D., Cornell University, 1951

tEugene P. Colton, Ph.D., University of California, Los Angeles, 1968

*Edwin A. Crosbie, Ph.D., University of Pittsburgh, 1952

Cary N. Davids, Ph.D., California Institute of Technology, 1967

Alexander J. Elwyn, Ph.D., Washington University, 1956

I Melvin S. Freedman, Ph.D., University of Chicago, 1942

Stuart J. Freedman, Ph.D., University of California, 1972

Gerald T. Garvey, Ph.D., Yale University, 1962

Donald F. Geesaman, Ph.D., State University of New York,

Stony Brook, 1976

**Walter F. Henning, Ph.D., Technical University, Munich, 1968

ttRobert E. Holland, Ph.D., University of Iowa, 1950

Roy J. Holt, Ph.D., Yale University, 1972

$*Harold E. Jackson, Jr., Ph.D., Cornell University, 1959

*In charge of tandem-superconducting linac operations and the ATLAS project.

tAccelerator research group. Joined the Physics Division October 1, 1982.

No longer at Argonne as of November 1982. Present address: Los Alamos

National Laboratory, Los Alamos, New Mexico.

Accelerator research group. Joined the Physics Division October 1, 1982.

In charge of Dynamitron accelerator operations. No longer at Argonne

as of November 1982. Present address: Fermi National Accelerator

Laboratory, Batavia, Illinois.

IIRetired - research participant.

Joint appointment with the University of Chicago.

Temporarily assigned to Technical University of Munich, Germany

(September 1982--September 1983).

ttRetired - research participant.

**In charge of Design Project for the GeV Electron Microtron.

266

Robert V. Janssens, Ph.D., Universite Catholique de Louvain,

Belgium, 1978

Tat K. Khoe, Ph.D., Technische Hogeschool Delft, Netherlands, 1960

Teng Lek Khoo, Ph.D., McMaster University, 1972

Dennis G. Kovar, Ph.D., Yale University, 1971

Victor E. Krohn, Ph.D., Case Western Reserve University, 1952

Robert L. Kustom, Ph.D., University of Wisconsin, 1969

Walter Kutschera, Ph.D., University of Graz, Austria, 1965

tAlexander Langsdorf, Jr., Ph.D., Massachusetts Institute of Technology,

1937

Richard C. Pardo, Ph.D., University of Texas, 1976

Karl Ernst Rehm, Ph.D., Technical University, Munich, 1973

tG. Roy Ringo, Ph.D., University of Chicago, 1940

*John P. Schiffer, Ph.D., Yale University, 1954

Kenneth W. Shepard, Ph.D., Stanford University, 1970

Lester C. Welch, Ph.D., University of Southern California, 1970

Jan L. Yntema, Ph.D., Free University of Amsterdam, 1952

Benjamin Zeidman, Ph.D., Washington University, 1957

THEORETICAL NUCLEAR PHYSICS

IlArnold F. Bodmer, Ph.D., Manchester University, 1953

Fritz Coester, Ph.D., University of Zurich, 1944

Benjamin Day, Ph.D., Cornell University, 1963

Dieter Kurath, Ph.D., University of Chicago, 1951

Robert D. Lawson, Ph.D., Stanford University, 1953

*Accelerator Research Group. Joined the Physics Division

October 1, 1982.

tRetired - research participant.

*Associate Director of the Physics Division; Director through

September 1982. Joint appointment with the University of Chicago.

Joined the Physics Division December 13, 1982.

IIJoint appointment with the University of Illinois, Chicago Circle Campus.

267

Tsung-Shung Harry Lee, Ph.D., University of Pittsburgh, 1973

*James E. Monahan, Ph.D., St. Louis University, 1951

tMurray Peshkin, Ph.D., Cornell University, 1951

Steven C. Pieper, Ph.D., University of Illinois, 1970

ATOMIC AND MOLECULAR PHYSICS

Joseph Berkowitz, Ph.D., Harvard University, 1955

H. Gordon Berry, Ph.D., University of Wisconsin, 1967

Kwok-tsang Cheng, Ph.D., University of Notre Dame, 1977

William J. Childs, Ph.D., University of Michigan, 1956

Donald S. Gemmell, Ph.D., Australian National University, 1960

Leonard S. Goodman, Ph.D., University of Chicago, 1952

Elliot P. Kanter, Ph.D., Rutgers University, 1977

I Gilbert J. Perlow, Ph.D., University of Chicago, 1940

Dieter Schneider, Ph.D., Free University of Berlin, 1945

SURFACE SCIENCE--FUSION POWER

"Manfred S. Kaminsky, Ph.D., University of Marburg, 1957

ADMINISTRATIVE STAFF

F. Paul Mooring, Ph.D., University of Wisconsin, 1951

ttJames R. Specht, A.A.S., DeVry Technical Institute, 1964

qOn disability status due to illness.

Deputy Director of the Physics Division.

Temporarily assigned to Laboratoire Aims Cotton, C.N.R.S., Orsay,

France (November 1981--April 1982).

Director of the Physics Division; Associate Director through

September 1982.

IIJoint appointment as Editor of Applied Physics Letters.

Transferred to ANL Materials Science and Technology Division, October 1982.

**Assistant Director of the Physics Division. Retired February 1983.

ttAssistant Director of the Physics Division since March 1, 1983.

268

TEMPORARY APPOINTMENTS

Postdoctoral AppointeesPartha Chowdhury (from State University of New York, Stony Brook,

New York): Gamma-ray spectroscopic studies of high angularmomentum properties in nuclei. (November 1979--January 1983)

David R. Cok (from Harvard University, Cambridge, Massachusetts):

RF and laser spectroscopy of molecular and ionic beams. (September1980--August 1982)

*Bradley W. Filippene (from University of Chicago, Chicago, Illinois):

Nuclear astrophysics research. (December 1982--January 1983)

tCarl A. Gagli di (from Princeon University, Princeton, New Jersey):Study of C beta decay: N(O ) s-decay experiment; design ofneutrino oscillation experiment instrumentation. (June 1982--

August 1982)

William S. Freeman (from State University of New York, Stony Brook,New York): Experimental heavy-ion and charged-particle nuclearphysics. (December 1980-- )

Thomas J. Humanic (from University of Pittsburgh, Pittsburgh,Pennsylvania): Experimental nuclear physics: heavy-ion reactions(transfer, fusion, incomplete fusion, etc.) using Argonne Tandem-Linac. (Argonne 1980--July 1982)

William E. Kleppinger (from Stanford University, Stanford, California):Theory of electromagnetic and weak interactions in nuclearphysics. (November 1982--- )

Wolfgang Kuhn (from Max-Planck-Institut fur Kernphysik, Heidelberg,Germany): Heavy-ion nuclear physics. (May 1981--November 1982)

*Raymond E. Kutina (from University of Toronto, Toronto, Canada):

Photoionization of free radicals. (March 1980--February 1983)

Alan Minchinton (from Flinders University, Adelaide, Australia):Collisional effects in the passage of fast molecular ions through

thin foils and gases. (December 1982-- )

*Formerly Resident Student Associate (Thesis), July 1979 through

December 1982. Ph.D., University of Chicago, 1983.

tFormerly Resident Student Associate (Thesis), July 1977 through

May 1982. Ph.D., Princeton University, 1982.

*No longer at Argonne as of February 28, 1983.

269

James J. Napolitano (from Stanford University, Stanford, California):Experimental studies of weak interactions and associated topics.(May 1982-- )

Ronald S. Pandolfi (from University of California, Los Angeles,California): UV-laser photofragmentation of molecular ions.(December 1982-- )

John A. Parmentola (from Massachusetts Institute of Technology,Cambridge,

Massachusetts): Theoretical research on chiral bag models in thestrong coupling approximation and high-energy proton nucleusscattering. (August 1980-- September 1982)

Volker H. Pfeufer (University of Hannover, Germany): RF laserspectroscopy on atoms, molecules, and ions. (July 1982-- )

Branko M. Ruscic (from Rudjer Boskovic Institute, Zagreb, Yugoslavia):Photoionization and photoelectron spectroscopy. (September 1981--

)

Lawrence P. Somerville (from Lawrence Livermore Laboratory, Livermore,California): Accelerator-based atomic physics: beam-foilspectroscopy; fast laser-ion beam interactions. (January 1983--

)

George S. Stephans (from University of Pennsylvania, Philadelphia,Pennsylvania): Nuclear physics using heavy-ion beams from the ANLlinac. (November 1982-- )

Kenneth E. Stephenson (from University of Wisconsin, Madison,Wisconsin):

Experimental photonuclear and intermediate energy nuclearphysics. (September 1979--July 1982)

Ernst Ungricht (from Eidgenossische Technische Hochschule, Zurich):Medium-energy pion scattering. (November 1982-- )

Robert B. Wiringa (from Los Alamos National Laboratory, Los Alamos,New Mexico): NN interaction, three-body forces, many-body theoryfor light nuclei, nuclear matter and neutron stars. (January 1981-

- )

Long-Term Visitors (at Argonne more than 4 months)

Daniel Ashery (Tel Aviv University, Ramat Aviv, Israel): Experimentalstudies of intermediate energy nuclear physics. (August 1980--October 1982)

270

*Dieter Frekers (University of Munster, Munster, West Germany):

Experimental heavy-ion and charged-particle nuclear physics.(December 1981-- )

tHiroshi Ikezoe (Japan Atomic Energy Research Institute, Tokai-Mura,Japan): Study of the nuclear reaction mechanism induced by the

energetic heavy-ion beams. (October 1982-- )

Hiroshi Kudo (University of Tsukuba, Japan): Accelerator-based atomic

physics. (December 1982-- )

David C. Radford (from Yale University, New Haven, Connecticut):Research on high spin states and heavy-ion reactions. (February1983-- )

$GuntherU. H. Rosner (Max-Planck-InsLitut fur Kernphysik, Heidelberg,Germany): Heavy-ion physics; reaction mechanisms; fusion and

heavy-ion reactions; charged-particle observation; Y-raydeexcitation. (June 1982-- )

tSuehiro Takeuchi (Japan Atomic Energy Research Institute, Tokai-Mura,Japan): Investigation of superconducting linac technology.

(October 1982-- )

Resident Graduate Students

Philip W. Arcuni (University of Chicago, Chicago, Illinois): Electronspectroscopy of ion-atom collisions. (October 1981-- )

Jordan B. Camp (University of Chicago, Chicago, Illinois): Weakinteractions. (October 1982-- )

Rollin M. Evans (Iowa State University, Ames, Iowa): On-line laserspectroscopy of radioactive atoms using the superconductinglinac. (March 1981-- )

Bradley W. Filippone (University of Chicago, Chicago, Illinois):Nuclear astrophysics research. (June 1979--December 1982)

Miles A. Finn (University of Minnesota, Minneapolis, Minnesota):On-line laser spectroscopy of radioactive atoms using thesuperconducting linac. (April 1981-- )

*Deutsche Forschungsgemeinschaft Fellowship.

tU.S.--Japan Collaboration for Nuclear Physics.

$Alexandervon Humboldt Foundation Fellow.

Postdoctoral appointee from December 1982 through January 1983.

271

Carl A. Gagliardi (Pknceton University, Princeton, New Jersey):C beta decay; N(O) -decay experiment; design of neutrino

oscillation experiment instrumentation. (July 1977--May 1982)

Jonathan E. Hardis (University of Chicago, Chicago, Illinois):Ion-ion and ion-atom collisions. (October 1979-- )

Alexandra R. Heath (University of Chicago, Chicago, Illinois): Weakinteractions in nuclear physics. (January 1979-- )

Michael A. Kroupa (University of Chicago, Chicago, Illinois): Searchfor magnetic monopoles using a plastic scintillator array.(July 1982-- )

Wolfram Stoffler (Freie Universitgt, Berlin, Germany): Electronspectroscopy with laser and fast ion-beam interaction.(July 1982-- )

Short-Term Visitors (at Argonne less than 4 months)

A. Faculty

Ademola Amusa (University of Ife, Ile-Ife, Nigeria,2efrica):Shell-model calculations in some nuclei (e.g., 0). (September1982--November 1982)

Reinhard Bruch (Universitst Freiburg, Freiburg, Germany): Electronspectroscopy. (July 1982--October 1982)

Wu Chieh Cheng (Paine College, Augusta, Georgia): High resolutionspectroscopy of ions using lasers (June 1982--August 1982)

Patrick J. Cooney (Millersville State College, Millersville,Pennsylvania): Studies of the interaction of fast-moving ions with

matter. (May 1982--July 1982)

Alan K.Edwards (University of Georgia, Athens, Georgia): UV-laserphoto-fragmentation of molecular ions. (June 1982--August 1982)

Hans Emling (Gesellschaft fur Schwerionenforschung, Darmstadt,Germany): Y spectroscopy of high spin states. (April 1982--June1982)

Geert Jonkers (Free University, Amsterdam, The Netherlands):Photoelectron spectroscopy of short-lived high-temperature species,

especially development of double oven techniques. (May 1982--September 1982)

*Postdoctoral appointee from June 1982 through August 1982.

272

John C. Kelly (University of New South Wales, Australia): Developmentof ion optics for atomic physics and Dynamitron applications.(June 1982--September 1982)

Michael J. King (Michigan State University, East Lansing, Michigan):Relativistic effects in fermionic states--a consistent treatment;connection between the relativistic constraint approach and the

quasipotential method. (July 1982--September 1982)

Stephen Landowne (University of Munich, Munich, Germany):Semimicroscopic and coupled-channel calculations of heavy-ionreactions. (April 1982)

David A. Lewis (Iowa State University, Ames, Iowa): On-line laserspectroscopy of radioactive atoms using the superconducting linac.

*Harry J. Lipkin (Weizmann Institute of Science, Rehovot, Israel):

Angularmomentum in electromagnetic fields of solenoids andmonopoles; applications of the constituent quark model to hadron

spectroscopy. (June 1982--November 1982)

A. Eugene Livingston (University of Notre Dame, Notre Dame, Indiana):Beam-foil spectroscopy of highly-ionized atoms. (August 1982)

Xiuzeng Ma (Institute of Atomic Energy, Beijing, China):Ultrasensitivemass spectrometry. (January 1983--February 1983)

Michael Paul (Hebrew University, Jerusalem, Israel): Accelerator-massspectrometry. (January 1983--September 1982)

P. R. Ramanujam (University of Toledo, Toledo, Ohio): High resolutionspectroscopy of ions using lasers. (August 1982--September 1982)

Ralph E. Segel (Northwestern University, Evanston, Illinois): Nuclearphysics research. (August 1982--September 1982)

Malcolm F. Steuer (University of Gerogia, Athens, Gerogia): Analysisof N2+ molecular ions' stopping power in carbon foils.(June 1982--August 1982)

Zeev Vager (Weizmann Institute of Science, Rehovot, Israel):Population of Rydberg states by swift ions after carbon targets.

(July 1982--October 1982)

*Joint appointment with Argonne High Energy Physics Division and with

Fermi National Accelerator Laboratory, Batavia, Illinois.

273

J. Dirk Walecka (Stanford University, Stanford, California):Scattering of energetic electrons by nuclei. (October 1982--January 1983)

B. Graduate Students

Edward A. Johnson (Oxford University, Oxford, England): Analysis ofmolecular-ion stopping power data and the development of a heavy-ion wake. (June 1982--July 1982)

Robert M. Panoff (Washington University, St. Louis, Missouri): Ground-state energetics of spin-aligned deuterium. (May 1982--August1982)

C. Undergraduate Students

James W. Bales (North Carolina State University, Raleigh, NorthCarolina).

(June 1982--August 1982)

Todd A. Drumm (Westminster College, New Wilmington, Pennsylvania).(January 1983-- )

Dana S. Fine (Stanford University, Stanford, California). (June 1982--August 1982)

James J. Hofmann (East Stroudsburg State College, East Stroudsburg,Pennsylvania) (January 1982--July 1982)

Arnold Kravitz (University of Hartford, West Hartford, Connecticut).(June 1982--August 1982)

John E. Tkaczyk (Rutgers State University, New Brunswick, New Jersey).(June 1982--August 1982)

David B. Young (Hope College, Holland, Michigan). (January 1983-- )

*Argonne Fellow.

274

TECHNICAL AND ENGINEERING STAFF

Ralph Benaroya

Peter J. Billquist

John M. Bogaty

*Patric K. Den Hartog

William F. Evans

John P. Greene

tJoseph E. Kulaga

Bruce G. Nardi

Robert W. Nielsen

Walter Ray, Jr.

James R. Specht

George E. Thomas, Jr.

James N. Worthington

Jerome R. Wrobel

UBruce J. Zabransky

Gary P. Zinkann

* In charge of Tandem accelerator operations.

tNo longer in the Physics Division as of May 1982. Now in the Chemical

Technology Division.

Assistant Division Director as of March 1, 1983.

In charge of Dynamitron accelerator operations.

275

Distribution for ANL-83-25

Internal:

R. AveryE. S. BeckjordL. BurrisD. W. CisselP. M. DehmerM. Derrick

R. E. DieboldD. R. FergusonM. S. Freedman

A. Friedman

B. R. T. FrostT. L. GilbertP. F. GustafsonE. HubermanM. Inokuti

J. H. KittelK. L. KliewerC. E. KlotzA. B. Krisciunas (12)L. G. LeSageR. A. Lewis

P. MessinaE. G. PewittJ. J. Roberts

J. RundoJ. E. SchofieldR. W. SpringerE. P. SteinbergD. Streets

C. E. TillJ. UnikS. WexlerR. S. Zeno

A. AmusaP. W. Arcuni

R. BenaroyaJ. BerkowitzH. G. Berry

A. R. BodmerL. M. BollingerJ. B. CampK.-T. ChengW. J. ChildsF. Coester

E. A. CrosbieC. N. DavidsB. DayP. K. Den HartogDynamit ronS. J. FreedmanW. S. Freeman

D. FrekersG. T. GarveyD. F. GeesamanD. S. GemmellL. S. GoodmanJ. E. HardisA. HeathW. HenningR. J. HoltH. IkezoeH. E. JacksonR. V. JanssensM. S. KaminskyE. P. KanterT. K. KhoeT. L. KhooW. E. KleppingerD. G. KovarV. E. KrohnM. A. KroupaH. KudoD. KurathR. L. Kustom

W. Kutschera

R. D. Lawson

T.-S. H. LeeA. MinchintonJ. E. MonahanJ. J. NapolitanoU. NielsenR. S. PandolfiR. C. PardoG. J. PerlowM. Peshkin (65)V. PfeuferS. C. PieperD. C. RadfordW. H. RauckhorstK. E. RehmG. R. RingoG. RosnerB. M. RuscicJ. P. SchifferK. W. ShepardR. K. SmitherL. P. SomervilleJ. R. SpechtG. S. StephansW. StofflerS. TakeuchiK. J. ThayerG. E. ThomasE. UngrichtL. WelchR. B. WiringaJ. N. WorthingtonJ. L. YntemaB. ZabranskyB. ZeidmanANL Patent Dept.

ANL Contract FileANL LibrariesTIS Files (6)

External:

DOE-TIC, for distribution per UC-34 (99)Manager, Chicago Operations Office, DOEW. J. McGonnagle, New Brunswick Lab., DOEPhysics Division Review Committee:

E. G. Adelberger, U. WashingtonJ. D. Fox, Florida State U.V. W. Hughes, Yale U.J. R. iuizenga, U. RochesterD. F. Measday, U. British ColumbiaJ. W. Negele, Massachusetts Inst. TechnologyA. Z. Schwarzschild, Brookhaven National Lab.J. J. Wynne, IBM Thomas J. Watson Research Center

276

F. Ajzenberg-Selove, U. Pennsylvania

R. G. Alias, U. S. Naval Research Lab.J. D. Anderson, Lawrence Livermore National Lab.

Antioch College, Olive Kettering Library, Antioch, Ill.P. Axel, U. IllinoisP. D. Barnes, Carnegie-Mellon U.

H. H. Barschall, U. Wisconsin-Madison

C. H. Batson, Bolingbrook, Ill.B. Bayman, U. Minnesota

G. B. Beard, Wayne State U.G. L. Bennett, Div. Reactor Safety Research, USNRC

C. H. Blanchard, U. Wisconsin-MadisonR. L. Boudrie, Los Alamos National Lab.

T. J. Bowles, Los Alamos National Lab.

D. A. Bromley, Yale U.

Brooklyn College, Dept. of PhysicsG. E. Brown, SUNY at Stony BrookS. B. Burson, Office of Nuclear Regulatory Research, USNRCD. L. Bushnell, Northern Illinois U.

F. R. Buskirk, U. S. Naval Postgraduate SchoolD. J. Buss, Illinois Benedictine CollegeL. E. Campbell, Hobart & William Smith CollegesP. Caruthers, Los Alamos National Lab.

Catholic University of America, Keane Physics Research Center

J. Cerny III, Lawrence Berkeley National Lab.

Chemical Abstracts Service, Columbus

G. F. Chew, Lawrence Berkeley National Lab.

W. A. Chupka, Yale U.Cincinnati, U. of, Physics LibraryJ. W. Clark, Washington U.C. M. Class, Rice U.

T. B. Clegg, U. North CarolinaH. Cohen, California State U., Los AngelesS. Cohen, Speakeasy Computing Corp., ChicagoD. R. Cok, Eastman Kodak Research Labs., Rochester, N.Y.Colorado, U. of, Nuclear Physics Lab.P. J. Cooney, Millersville State College, Millersville, Pa.Cornell U., LibraryN. Cue, SUNY at AlbanyK. Daneshvar, U. Pennsylvania

S. E. ,Darden, U. Notre Dame

Dartmouth College, Library

S. K. Das, Pratt and Whitney Aircraft Group, West Palm BeachP. T. Debevec, U. IllinoisD. Dehnhard, U. MinnesotaDenver, U. of, Physics Dept.R. DeSerio, U. A '.zonaR. M. DeVries, Los Alamos National Lab.B. Donnally, Lake Forest College, Lake Forest, Ill.T. R. Donoghue, Ohio State U.P. J. Dusza, Physics Equipment, Midlothian, Ill.A. K. Edwards, U. Georgia

277

A. J. Elwyn, Fermi National Accelerator Lab.G. N. Epstein, Massachusetts Inst. TechnologyU. Fano, U. ChicagoB. W. Filippone, California Inst. TechnologyH. J. Fischbeck, U. OklahomaP. A. Flinn, Intel Corp., Santa ClaraFord Aerospace and Communications Corp., Newport Beach, Calif.H. T. Fortune, U. PennsylvaniaJ. L. Fowler, Oak Ridge National Lab.W. A. Fowler, California Inst. TechnologyC. A. Gagliardi, Texas A&M U.P. W. Gilles, U. KansasN. K. Glendenning, Lawrence Berkeley National Lab.H. Goldstein, Columbia U.H. E. Gove, U. RochesterW. Haeberli, U. Wisconsin, MadisonI. Halpern, U. Washington

M. Hamermesh, U. MinnesotaS. S. Hanna, Stanford U.A. 0. Hanson, U. IllinoisR. R. Hart, Cambridge, Mass.B. G. Harvey, Lawrence Berkeley National Lab.M. Hasan, Northern Illinois U.A. J. Hatch, ChicagoH. G. Heard, Woodside, Calif.D. W. Heikkinen, Lawrence Livermore National Lab.R. G. Helmer, EG&G Idaho, Inc.E. M. Henley, U. WashingtonR. G. Herb, National Electrostatics Corp., Middleton, Wis.R. E. Holland, Downers Grove, Ill.R. E. Honig, RCA Labs., Princeton, N. J.J. T. Hood, Washington U.T. J. Humanic, U. S. Naval AcademyW. A. Huston, Hammond, Ind.IIT Research Institute, Physics Library, ChicagoIllinois, U. of, Chicago Circle, Dept. of PhysicsIndiana U., Cyclotron ProjectM. Inghram, U. ChicagoD. R. Inglis, U. MassachusettsInstitute for Advanced Study, Physics Preprint Library, PrincetonC. M. Jachcinski, Bell Labs., Naperville, Ill.P. B. Kahn, SUNY at Stony BrookR. J. Kandel, Office of Basic Energy Sciences, USDOEJ. C. Kelly, Arizona State U.A. K. Kerman, Massachusetts Inst. TechnologyM. J. King, Sohio Technical Center, ClevelandB. B. Kinsey, U. of Texas at AustinE. A. Knapp, Los Alamos National Lab.N. Koller, Rutgers U.F. T. Kuchnir, Elmhurst, Ill.J. E. Kulaga, Naperville, Ill.J. W. Lamka, C-E Raymond Combustion Engineering, Inc., ChicagoR. 0. Lane, Ohio U.A. Langsdorf, Jr., Schaumburg, Ill.

278

R. M. Laszewski, U. Illinois, Urbana

L. L. Lee, Jr., SUNY at Stony BrookJ. J. Livingood, Hinsdale, Ill.A. E. Livingston, U. Notre DameL. F. Long, U. Notre DameG. D. Loper, Wichita State U.Louisiana State U., Dept. of Physics and Astronomy, LibrarianLouisiana State U., Director, Nuclear Science CenterM. H. Macfarlane, Indiana U.A. P. Magruder, EG&G, Las Vegas, Nev.J. V. Maher, U. PittsburghM. Maier, Lawrence Berkeley National Lab.J. Margrave, Rice U.Marquette U., Physics Dept., MilwaukeeJ. V. Martinez, Office of Basic Energy Sciences, USDOEMaryland, U. of, Dept. of Physics and Astronomy, Preprint Lib.Massachusetts Inst. Technology, Physics Reading RoomD. A. McClure, Applied Physical Technology, Inc., Smyrna, Ga.J. C. McDonald, Sloan-Kettering Inst.R. D. McKeown, California Inst. TechnologyG. W. Meisner, U. North CarolinaMichigan State U., Cyclotron Lab., LibrarianMississippi, U. of, LibraryA. Moen, Central College, Pella, Ia.C. F. Moore, U, of Texas at AustinF. P. Mooring, Glen Ellyn, Ill.H. T. Motz, Los Alamos National Lab.M. Murphy, Lawrence Berkeley National Lab.Y. Nakamura, Jet Propulsion Lab.A. I. Namenson, Naval Research Lab.H. Newson, Duke U.New York U. Medical Center, Environmental Medicine Lib., TuxedoJ. A. Nolen, Jr., Michigan State U.E. B. Norman, U. Washington

C. Olmer, Indiana U.W. K. H. Panofsky, Stanford Linear Accelerator CenterJ. T. Park, U. Missouri-RollaL. A. Parks, Florida State U.J. A. Parmentola, U. PittsburghE. S. Pierce, Office of Basic Energy Sciences, USDOER. E. Pollock, Indiana U.R. S. Preston, Northern Illinois U.F. W. Prosser, U. KansasS. Raboy, Harpur College, SUNY, BinghamtonJ. L. Rainwater, Columbia U., IrvingtonP. S. Ramanujam, U. ToledoA. J. Ratkowski, Hanscom AFB, Mass.G. Reynolds, Palmer Physics Lab., Princeton U.M. Rhoades-Brown, Oak Ridge National Lab.R. G. H. Robertson, Los Alamos National Lab.Rochester, U. of, Physics/Optics/Astronomy Lib.N. P. Samios, Brookhaven National Lab.S. J. Sanders, Yale U.R. P. Scharenberg, Purdue U.

279

R. M. Schectman, U. ToledoP. D. Schnur, Charles B. Chrystal Co., New York CityR. E. Segel, Northwestern U.F. J. D. Serduke, Lawrence Livermore National Lab.K. K. Seth, Northwestern U.

S. M. Shafroth, U. North CarolinaR. Sherr, Palmer Physics Lab., Princeton U.C. G. Shull, Massachusetts Inst. TechnologyH. Shwe, East Stroudsburg State College, East Stroudsburg, Pa.C. E. Skov, Monmouth CollegeC. P. Slichter, U. IllinoisH. E. Stanton, Oak Lawn, Ill.

N. B. Stearns, Ford Scientific Lab.N. Stein, Yale U.P. H. Stelson, Oak Ridge National Lab.E. J. Stephenson, Indiana U.K. E. Stephenson, Princeton U..I. F. Steuer, U. Georgia

J. Stoltzfus, Beloit CollegeW. G. Stoppenhagen, Ohio U., LancasterT. T. Sugihara, Texas A&M U.M. Svonavec, Purdue U., Calumet CenterS. L. Tabor, U. MarylandH. Takeda, K.M.S. Fusion Inc., Ann Arbor, Mich.R. F. Taschek, Los Alamos National Lab.C. C. Trail, Brooklyn CollegeR. Vandenbosch, U. WashingtonS. E. Vigdor, Indiana U.C. M. Vincent, U. PittsburghD. H. Vincent, U. MichiganJ. D. Walecka, Stanford U.T. P. Wangler, Los Alamos National Lab.B. A. Watson, Stanford U.L. Weaver, Kansas State U.G. H. Wedberg, Gaithersburg, Md.M. J. Weiss, U. NebraskaV. Weisskopf, Massachusetts Inst. TechnologyK. J. Wetzel, U. PortlandW. R. Wharton, Carnegie-Mellon U.M. G. White, Princeton U.E. P. Wigner, Princeton U.H. B. Willard, Case Western Reserve U.Wisconsin, U. of, Physics Library, MadisonG. T. Wood, Cleveland State U.C. S. Wu, Columbia U.0. K. Wu, Gould Inc., Rolling Meadows, Ill.A. J. F. Boyle, U. Western Australia, NedlandsL. T. Chadderton, David Rivett Lab., Clayton, AustraliaJ. 0. Newton, Australian National U., CanberraT. R. Ophel, Australian National U., CanberraL. J. Tassie, Australian National U., CanberraE. W. Titterton, Australian National U., CanberraW. Kerber, Zentralbibliothek d. Physik Inst., Vienna, AustriaEuratom, Central Bu. Nuclear Measurements, Library, Geel, Belgium

280

Katholieka Universiteit Leuven, Inst. voor Theoretische Fysica, Heverlee, BelgiumJ. Vervier, U. Catholique de Louvain, BelgiumBrasilia, Universidade de, Inst. Central de Fisica, BrazilDivisao de Estudos Avancados, San Jose dos Campos, Brazil0. Sala, Universidade de Sao Paulo, BrazilSao Paulo, Universidade de, Nuclear Physics Lab., Pelletron Lab., BrazilUniversidade Federal de Pernambuco, Recife, BrazilAlberta, U. of, Nuclear Research Centre, Dept. of Physics, Edmonton, CanadaG. A. Bartholomew, Atomic Energy Canada Ltd., Chalk River, CanadaR. L. Brooks, U. Guelph, CanadaH. C. Evans, Queens U., Kingston, CanadaT. J. Kennett, McMaster U., Hamilton, CanadaJ. D. Kurbatov, Victoria, Canada

McGill U., Lib., Rutherford Physics Bldg., Montreal, CanadaJ. C. D. Milton, Chalk River Nuclear Labs., CanadaG. C. Nielson, U. Alberta, Edmonton, CanadaW. V. Prestwich, McMaster U., Hamilton, CanadaW. J. Romo, Carleton U., Ottawa, CanadaJ. L. Whitton, Queen's U., Kingston, CanadaL. Gomberoff, Universidad de Chile, Santiago, ChileD. Dazhao, Beijing, People's Republic of ChinaY-z. Gu, Fudan University, Shanghai, People's Republic of ChinaJ-s. Maa, National Tsing-Hua U., Hsinchu, Republic of ChinaP-K. Tseng, National Taiwan U., Taipei, Republic of ChinaA. Bohr, Inst. for Theoretical Physics, Copenhagen, DenmarkJ. Borggreen, Niels Bohr Inst., Roskilde, DenmarkP. Chowdhury, Niels Bohr Inst., Roskilde, DenmarkC. J. Christensen, Danish AEC, Rise, DenmarkB. R. Mottelson, Inst. for Theoretical Physics, Copenhagen, DenmarkNiels Bohr Inst., The Library, Copenhagen, Denmark0. Poulsen, U. Aarhus, DenmarkF. El Bedewi, Atomic Energy Establishment, Cairo, EgyptM. El Nadi, Cairo U., EgyptI. Hamouda, Atomic Energy Establishment, Cairo, EgyptA. Osman, Cairo U., EgyptBerkeley Nuclear Labs., Central Electricity Generating Bd., Librarian, EnglandJ. B. Birks, The University, Manchester, EnglandCulham Lab., UKAEA, Librarian, EnglandN. Daly, UKAWRE, Aldermaston, EnglandJ. H. D. Eland, U. Oxford, EnglandA. T. G. Ferguson, AERE, Harwell, EnglandM. Grace, Oxford U., EnglandC. E. Johnson, U. Liverpool, EnglandJ. S. Lilley, Daresbury Lab., EnglandG. C. Morrison, U. Birmingham, EnglandR. S. Nelson, AERE, Harwell, EnglandJ. C. C. Sharp, Daresbury Lab., Warrington, EnglandSussex, U. of, Library, Brighton, EnglandM. W. Thompson, U. Sussex, Brighton, EnglandUniversity College London, Library, Dept. of Physics and Astronomy, EnglandJ. Walker, U. Birmingham, EnglandJ. C. Willmott, The University, Manchester, EnglandK. V. Laurikainen, U. Helsinki, FinlandA. Abragam, CEN Saclay, France

281

P. Catillion, CEN Saclay, FranceCEA Saclay, Library, FranceCentre de Recherches Nucleaires, Strasbourg, FranceC.N.R.S., Centre de Physique Theorique, Preprint Lib., Marseille, FranceJ. Delaunay, CEN Saclay, FranceH. Ekstein, C.N.R.S., Marseille, FranceInst. de Physique Nucleaire, Lib., U. Paris, Orsay, FranceInstitut des Sciences Nucleaires, Lib., Grenoble, FranceLaboratoire de l'Accelerateur Lineaire, U. Paris, Orsay, FranceA. Michaudon, C.E.A., Centre d'Etudes de Bruyeres le Chatel, Montrouge, FranceH. Nifenecker, CEN Grenoble, FranceJ. C. Poizat, U. Claude Bernard, Villeurbanne, FranceJ. M. Remillieux, U. Claude Bernard, Villeurbanne, FranceR. Seltz, Centre de Recherches Nucleaires, Strrsbourg, FranceJ. C. Sens, Centre de Recherches Nucleaires, Strasbourg, FranceK. Bethge, Inst. f. Kernphysik, Universitat, Frankfurt, GermanyR. Bock, GSI, Darmstadt, GermanyH. Bohn, Technische Universitat, Munich, GermanyDeutsches Elektronen-Synchrotron, Librarian, Hamburg, GermanyK. A. Eberhard, U. Munich, GermanyH. Ehrhardt, U. Kaiserslautern, GermanyA. A. Forster, Techn. U. Munchen, GermanyH. U. Gersch, Zfk Rossendorf, Dresden, GermanyGesellschaft fur Schwerionen-forschung mbH, Bibliothek, Darmstadt, GermanyK. Grabisch, Hahn-Meitner Inst., Berlin, Germany

K-0. Groeneveld, Universitat Frankfurt, GermanyD. Habs, Max-Planck Inst. fuer Kernphysik, Heidelberg, GermanyJ. W. Hammer, U. Stuttgart, GermanyP. Kienle, Technische Hochschule Munchen, GermanyH. V. Klapdor, Max-Planck Inst. f. Kernphysik, Heidelberg, GermanyH-J. Korner, Technische Universitat Munchen, GermanyW. KUhn, U. Giessen, GermanyH. G. Kimmel, Ruhr Universitat Bochum, GermanyL. Lassen, Universitat Heidelberg, GermanyN. Marquardt, Ruhr-Universitat Bochum, GermanyC. Mayer-Bricke, Kernforschungsanlage Julich, GermanyT. Mayer-Kuckuk, Universitat Bonn, GermanyU. B. Mosel, Universitat Giessen, GermanyA. Muller-Arnke, Technischen Hochschule, Darmstadt, Germany0. Osberghaus, Universitat Freiburg, GermanyW. J. Pietsch, U. Cologne, GermanyW. Potzel, Technical U. Munich, GermanyK. E. Rehm, Technische Universitat, Munich, GermanyA. Richter, Tech. Hochschule, Darmstadt, GermanyR. Santo, U. Munchen, GermanyD. Schneider, Hahn-Meitner-Inst., Berlin, Germany0. W. B. Schult, KFA Julich, GermanyP. Sperr, Hochschule d. Bundeswehr Munchen, Neubiberg, GermanyJ. Speth, Inst. fur Kernphysik der KFA, Julich, GermanyU. Strohbusch, Inst. fur Experimentalphysik Zyklotron, Hamburg, GermanyUniversitat Munchen, Library, Physik Dept., Garching, GermanyD. von Ehrenstein, U. Bremen, GermanyS. Wagner, Physikalisch-Technische Bundesanstalt, Braunschweig, GermanyG. Wortmann, Technical U. Munchen, Germany

282

J. G. Zabolitzky, Ruhr-Universitat, Bochum, GermanyG. Anagnostatos, N.R.C. Demokritos, Athens, GreeceN. Gangas, U. of Ioannina, GreeceA. Katsanos, NRC Democritos, Athens, GreeceJ. Cseh, Inst. Nuclear Research, Hungarian Ady. Sciences, Debrecen, HungaryN. Anantaraman, UEC Lab., Calcutta, IndiaBhabha Atomic Research Centre, Calcutta, India

M. R. Bhiday, U. Poona, IndiaS. Chakravarti, Jadavpur U., Calcutta, IndiaM. Ismail, Bhabha Atomic Research Centre, Calcutta, IndiaK. Mehta, Indian Inst. of Technology, Kanpur, India

N. Nath, Kurukshetra U., IndiaS. P. Pandya, Physical Research Lab., Ahmedabad, IndiaN. G. Puttaswamy, Bangalore U., IndiaN. N. Raina, U. Kashmir, IndiaI. Ramarao, Tata Inst. of Fundamental Research, Bombay, IndiaA. P. Shukla, Indian Inst. of Technology, Kanpur, IndiaP. C. Sood, Banaras Hindu U., Varanasi, IndiaIndonesia, U. of, Jakarta, IndonesiaA. A. Azooz, U. Mosul, IraqJ. Alster, Tel Aviv U., IsraelD. Ashery, Tel Aviv U., IsraelA. E. Blaugrund, Weizmann Inst. of Science, Rehovot, IsraelY. Eisen, Weizmann Inst. of Science, Rehovot, IsraelA. Marinov, Hebrew U., Jerusalem, IsraelM. Moinester, Tel Aviv U., Israel

Negev, U. of, Physics Preprint Library, Beer-Sheva, IsraelM. Paul, Hebrew U., Jerusalem, IsraelI. Plesser, Weizmann Inst. of Science, Rehovot, IsraelB. Rosner, Technion - Israel Inst. of Tech., Haifa, IsraelZ. Vager, Weizmann Inst. of Science, Rehovot, IsraelA. Weinreb, Hebrew U., Jerusalem, IsraelWeizmann Inst. of Science, Physics Library, Rehovot, IsraelN. Zeldes, Hebrew U., Jerusalem, IsraelC. Coceva, C.N.E.N., Bologna, ItalyInstituto di Fisica, Preprint Librarian, Torino, ItalyInstituto di Fisica dell Universita, Catania, Italy

Instituto de Fisica Sperimentale, c/o Dr. M. Vadacchino, Torino, ItalyInstituto Nazionale di Fisica Nucleare, Sezione di Pisa, ItalyInstituto Superiore di Sanita, Laboratorio della Radiazioni, Rome, ItalyM. Mando, Phys. Inst. of the University, Firenze, Italy

C. Signorini, Instituto di Fisica, Padova, ItalyY. Abe, Kyoto U., JapanK. Hiida, U. Tokyo, JapanT. Hirano, Hosei U., Tokyo, JapanK. Iwatani, Hiroshima U., JapanK. Katori, U. of Osaka, Japan

M. Kawai, Kyushu U., Fukuoka, JapanK. Kubodera, Sophia U., Tokyo, Japan

S. M. Lee, U. of Tsukaba, Ibaraki, JapanNagoya U., Dept. of Physics, Preprint Center, JapanG. Narumi, Hiroshima U., JapanH. Ohuuma, Tokyo Inst. Technology, Japan

K. Sugiyama, Tohoku U., Japan

283

Tokyo, U. of, High Energy Physics Lab., Japan

Tokyo, U. of, Inst. for Nuclear Study, Lib., JapanTokyo, U. of, Meson Science Lab., JapanK. Tsukada, Japan Atomic Energy Research Inst., Tokai, JapanY. S. Kim, Atomic Energy Research Institute, Seoul, KoreaKorea U., Physics Dept., Seoul, KoreaInstituto de Fisica, Theoretical Physics Grp., Preprint Lib., Mexico City,

Mexico

Instituto Politecnico Nacional Physics Dept. Lib., Mexico City, MexicoJ. Blok, Free U., Amsterdam, The NetherlandsJ. de Jager, Bibliotheek V.U., Natuurkunde, Amsterdam, The NetherlandsH. de Waard, Rijksuniversiteit, Groningen, The NetherlandsP. F. A. Goudsmit, Inst. for Nuclear Physics Research, Amsterdam,

The NetherlandsG. Jonkers, Free Univ., Amsterdam, The NetherlandsR. Kamermans, Graafflaboratorium, Utrecht, The NetherlandsKoninklijke Nederlandse Akademie van Wetenschappen, Library, Amsterdam,

The NetherlandsR. H. Siemssen, U. Groningen, The NetherlandsG. van Middelkoop, Vrije Universiteit, Amsterdam, The NetherlandsA. Vermeer, U. Utrecht, The NetherlandsA. Poletti, U. Auckland, New ZealandJ. F. Williams, Queens U., Belfast, Northern IrelandPakistan Inst. of Nuclear Science and Technology, Rawalpindi, PakistanQuaid e=Azam U., Dept. of Physics, Islamabad, PakistanQ. 0. Navarro, Philippine Atomic Research Center, Quezon City,

Philippine IslandsJ. Kuzminski, Inst. of Physics, Katowice, PolandW. Zych, Inst. of Nuclear Research, Warsaw, PolandF. da Silva, Lab. de Fisica e Engenharia Nucleares, Sacavem, PortugalInstitute for Physics and Nuclear Eng., Bucharest, Romania

Timisoara, U. of, Library, RomaniaD. Branford, U. Edinburgh, ScotlandD. H. Pringle, Nuclear Enterprises Ltd., Edinburgh, ScotlandE. Barnard, Atomic Energy Board, Pretoria, South AfricaF. D. Brooks, U. Cape Town, South AfrcaW. R. McMurray, Southern Universities Nuclear Inst., Faure, South AfricaD. W. Mingay, Atomic Energy Board, Pretoria, South AfricaD. Reitmann, National Accelerator Center, Faure, South AfricaJ. P. F. Sellschop, U. of the Witwatersrand, South Africa0. Almen, Chalmers U. of Technology, Gothenburg, SwedenI. Bergstrom, Nobelinstitut for Fysik, Stockholm, SwedenM. Braun, Research Inst. of Physics, Stockholm, SwedenN. Ryde, Chalmers U. of Technology, Gothenburg, SwedenTandem Accelerator Lab., Uppsala, SwedenJ. Rafelski, CERN, Geneva, SwitzerlandS. Ketudat, Chulalongkorn U., Bangkok, ThailandDiyarbakir U., D. U. Fen Fakultesi, TurkeyA. Saplakoglu, Ankara Nuclear Research and Training Center, Ankara, TurkeyA. J. Kalnay, IVIC, Physics Section, Caracas, Venezuelavenezuela, Universidad Central de, Physics Dept., Caracas, Venezuela

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