Examples of nuclear structure observables with fast beams Discovery of new isotopes

INPC 2007 –Slide 1

In-beam gamma-ray spectroscopy withfast beams of rare isotopes

Experiments to elucidate the structure of very exotic nuclei

Thomas GlasmacherNational Superconducting Cyclotron Laboratory

Michigan State University

1. Examples of nuclear structure observables with fast beams2. Discovery of new isotopes3. The boundaries of the Island of Inversion4. Collectivity in silicon and sulfur towards N=28


Goal: Develop predictive theory of atomic nuclei and their reactions

• Stable nuclei are well-described with closed-shell (so-called “magic”) nuclei as key benchmarks

• Rare isotopes show evidence for– disappearance of canonical shell

gaps,– appearance of new shell gaps,– reduction of spin-orbit force

• The most exotic nuclei accessible (largest N/Z ratio) are light nuclei and they have low beam rates

• New precision techniques have been developed in past decade to enable spectroscopy of these most exotic nuclei

• Experimental task: Quantify changes encountered in rare isotopes and measure with defined certainty observables that are calculable and can be used to discriminate between theories


In-flight production of rare isotopes

Driver accelerator (v = 0.25-0.6 c) Fragment separator (A1900 NSCL, FRS GSI, BigRIPS RIKEN, ALPHA spectrometer/LISE GANIL) Identification and beam transport

Stopped beam experiments, reaccelerated beam experiments Fast beam experiments

Secondary reaction Reaction product identification (S800 spectrograph, CATE/Aladin, Silicon telescopes/TOF wall, SPEG)

Fragment separator A1900 fragment separator

Identification and beam transport

Reaction product identification S800 spectrograph


In-flight production of rare isotopesExample: 78Ni from 86Kr at NSCL

Driver accelerator Fragment separator (A1900 NSCL, FRS GSI, BigRIPS RIKEN, ALPHA/LISE GANIL) Identification and beam transport

Stopped beam experiments Fast beam experiments

Secondary reaction Reaction product identification (S800 spectrograph, CATE/Aladin, Silicon telescopes/TOF wall, SPEG)

Fragments at focal plane

Fragments at production target

Fragments at achromatic degrader

65% of theproduced 78Nitransmitted


Examples of observables in experiments within-flight produced exotic beams

Rates are within 1-2 orders of magnitude depending on implementation and structure of nucleus

Stopped beam experiments• Possible experiments and quality Possible experiments and quality

of observables depend on number of observables depend on number of beam particlesof beam particles

• * Discovery (few particles total)

• Half live(few ten particles)

• Mass (few hundred particles)

Fast beam experiments• Possible experiments and quality Possible experiments and quality

of observables depend on of observables depend on luminosityluminosity

• Interaction radii(few particles per hour)

• g-factors(hundreds of particles per second)

Fast beam experiments (cont’d)• Excited state energies

– * Multi-nucleon removal(hundreds of particles per second)

• Excited state energies, transition matrix elements

– * Inelastic scattering: Coulomb excitation, p-, scattering(ten particles per second)

– Lifetimes from -ray line shapes(hundreds of particles per second)

• Occupation numbers– * Single nucleon removal

(particles per second)– Two-nucleon removal

(hundreds of particles per second)– * Nucleon addition

(hundreds of particles per second)


Fast-beam -ray spectroscopy at rates of a few nuclei per second

• NRNT × NB × – NR reaction rate (yields

observable)– NT atomic density of target– NB beam rate– cross section (given by

nature)

• Fast exotic beams allow for– event-by-event identification and

trigger– efficient detection of recoiling beam

particles due to kinematic focusing– thick secondary targets (100-1000

thicker than at low energy)• Strategy: Use of photons to indicate

inelastic scattering, measure particle- coincidences

• Example– = 100 mbarn– NT = 1021 cm-2

– NB = 3 Hz

– NR = 26/day = 3×10-4 Hz

beam targetscatteredbeam


Direct reactions with heavy ions and coincident -ray spectroscopy

M. Ishihara, Nucl. Phys. A 400 (1983) 153c


Direct reactions with heavy ions and coincident -ray spectroscopy

M. Ishihara, Nucl. Phys. A 400 (1983) 153c


Intermediate-energy Coulomb excitation of 32MgLarge transition matrix element indicates breakdown of the N=20 shell gap

Experiment:

Max. determines min. impact param.

T. Motobayashi et al., Phys. Lett. B 346 (1995) 9

T.G. Ann. Rev. Nucl. Part. Sci. 48 (1998) 1

Impact parameter

Scattering angle

Coul = 87 mb B(E2↑) = 454(78) e2fm4 = <0+||O(2)||2+>

Shell model

Valence nucleonmodel

20181614N 12


Intermediate-energy Coulomb excitation

• Active programs at GANIL, GSI, MSU and RIKEN

• Published measurements to elucidate N=8, 20, 28, 32, 34, N=Z=36, light tin isotopes, …

• Single-step process• Sensitive to E1, E2, E3

excitations• Results agree with prior

measurements where available

-50

-25

0

25

50

75

100

125

150

175

200

225

250

40Ar 36

Ar24

Mg30

S78

Kr 58Ni

76Ge

26Mg

Intermediate-energyCoulomb excitationAdopted value

Adopted and measured B(E2) values for stable nuclei

Adopted valueCoulomb excitationResonance fluorescenceDoppler shift attenuationRecoil distributionElectron scatteringIntermediate-energyCoulomb excitation

Mg26

B(E2) values fromdifferent methods for 26Mg

J. Cook et al., Phys. Rev. C 73 (2006) 024315.

Diff

. b

tw.

me

asu

red

an

d a

do

pte

d B

(E2)

(%

)


Wavefunction spectroscopy with knock-out reactions

• Shape of recoil momentum distribution of the A-1 fragment is measured and sensitive to l-value of knocked out nucleon

• Individual final states are tagged by -rays

• Spectroscopic factors are determined from the population of excited states in the A-1 fragment.

),(),(),(

),(),()( 2

ndiffrspn

stripspnsp

jnsp

BjBjBj

BjInjSCnI

P.G. Hansen and J. A. Tostevin, Ann. Rev. Nucl. Sci. 53 (2003) 219 P4-1 (Wed)


Breakdown of the N=8 shell gap in 12Be12Be ground state only 32% (1s1p)8 and 68% (1s1p)6-(2s,1d)2

1/2+

1/2-

5/2+ d5/2

p1/2 17.5(26) mb

s1/2 32.0(47) mb

12Be 11Be+n+


Exploring the boundaries of Island of Inversion

• C. Thibault et al: PRC 12 (1975) 64631,32Na, local increase of S2n N=20 shell gap decreased

• X. Campi et al: NPA 251(1975) 193explained by deformation via filling of (f7/2)

• C. Detraz et al: PRC19 (1979) 16432Na 32Mg decay, low 2+ in 32Mg

• E. Warburton et al: PRC 41 (1990) 1147Z=10-12 and N=20-22 have ground state wavefunctions dominated by (sd)-2(fp)+2 configurations

• T. Motobayashi et al: PLB 346 (1995) 9large B(E2;0+ 2+) in 32Mg

See also • V. Tripathi et al. Phys. Rev. Lett. 94 (2005)

162501 (2005)• G. Neyens et al. Phys. Rev. Lett. 94 (2005)

022501 (2005)• A. Obertelli et al., Phys. Lett B 633 (2006) 33 • H. Iwasaki et al., Phys.Lett. B 620 (2005) 118

• Single-neutron removal to look for negative parity states, indicating the presence of f7/2 intruder configurations in the ground state of the parent: (30Mg,29Mg+) (26Ne,25Ne+) (28Ne,27Ne+)

• (38Si,36Mg+) two-proton removal


Single-neutron removal from 26,28Ne and 30Mg

25Ne level structure known• A.T. Reed et al., PRC 60 (1999) 024311• S. Padgett et al., PRC 72 (2005) 064330

• 25Ne is well-described in sd shell with no evidence for intruder states below 3 MeV

→ No evidence for intruder configurations in the ground state wave function of 26Ne

J.R. Terry et al., Phys. Lett. B 640 (2006) 86

→ Island of inversion is growing


Proton scattering in inverse kinematics

• Many experiments at GANIL (MUST detector)

• Few experiments at MSU• Thin target to avoid angular and

energy straggeling of low-energy protons

p(56Ni,p’) at GSI G. Kraus et al., PRL 73 (1994) 1773

Normal kinematics

Inverse kinematics

F. Maréchal et al., PRC 60 (1999) 034615


Thick-target -tagged inelastic proton scattering Pioneering experiment at RIKEN p(30Ne,30Neg)

Y. Yanagisawa et al. PLB 566 (2003) 84

10

11

12

13

14

15

16

17

18

19

16 20 24 28

36Si setting

40Si setting

•

Inelastic p scattering using two cocktail beam settings to study chains of isotopes accessible in a consistent approach

Determine excited state energies and collectivity towards N=28 Univ. Tokyo, RIKEN, Rikkyo Univ., Michigan State Univ.

collaboration

40Si

N

Z

36Si

Sulfur

SiliconRIKEN/Kyushu/Rikkyo LH2 target:H. Ryuto et al., NIM A 555 (2005) 1

30 mm diameter 9 mm thick, nominal Negligible contaminant reactions

C.M. Campbell Ph.D. thesis (2007) Michigan State Univ.


Evolution of 2+ energies towards N=28

Above Z=20Ti, Cr and Fe

Below Z=20Si, S and Ar

40Si986(6) keV

• 1.5 million 40Si beam particles

• p,p’ = 20(3) mb

• ~30 counts in the photopeak• Low energy indicative of neutron

collectivity in 42Si

C.M. Campbell et al., PRL 97 (2006) 112501


Evolution of 2+ energies towards N=28

Above Z=20Ti, Cr and Fe

Below Z=20Si, S and Ar

40Si986(6) keV

• 1.5 million 40Si beam particles

• p,p’ = 20(3) mb

• ~30 counts in the photopeak• Low energy indicative of neutron

collectivity in 42Si

C.M. Campbell et al., PRL 97 (2006) 112501 Discovery of low-lying 2+ state in 42Si at GANIL B. Bastin, S. Grévy et al. arXiv 0705.4526 F9-2 (Wed)


Higher excited states in 40Si

• Two additional -rays in fragmentation channel 42P-p-n

– States at 1.62(1) MeV and 1.82(1) MeV?

• Not enough statistics to test if the two transitions are in coincidence

• Independent of the sequence, the second excited state is low in energy

• In the shell model second excited state is ph-excitation across N=28

• Low energy supports narrowing of the N=28 gap in 40Si

C.M. Campbell et al., PRL 97 (2006) 112501


1.5

2

2.5

3

3.5

20 22 24 26 28N

E(4

+1)

/ E(2

+1)

Sulfur

0.1

0.2

0.3

0.4

0.5

16 20 24 28

2| (p

,p')

Evolution and character of collectivity

Prior data from F. Maréchal et al, PRC 60, 034615 (1999)P.D. Cottle et al., PRL 88, 172502 (2002)

Silicon

0.1

0.2

0.3

0.4

0.5

16 20 24 28

2|

(p,p

')

NN

Rotational limit

Vibrational limit

Sulfur

Silicon

• Enhanced collectivity towards N=28 in silicon

• Sulfur transitions from vibrational mid-shell to rotational towards N=28

• Silicon vibrational mid-shell

C.M. Campbell Ph.D. thesis (2007) MSU


Single-proton addition

• Traditionally performed in normal kinematics at lower beam energies, e.g. (d,n), (3He,d), (,t), …

• Few mb cross sections observed at intermediate energies

• Proton well-bound in 9BeSp(9Be) = 16.9 MeV

• 8Li has only one bound excited state

Beam identification Reaction product identification


Measure coincident -rays and particle momenta


Resulting strength distribution compared to normal kinematics measurement

A.M. Mukhamedzhanov et al. Phys. Rev. C 73 (2006) 035806

A. Gade et al. in preparation (2007)


Structure of 23F: Multiple reactions in one experiment~35 MeV/nucl,100 mg/cm2 liquid helium target at RIKEN

A. Michimasa et al. Phys. Lett. B 638 (2006) 146

4He(22O,23F) 2000/sProton addition

4He(23F,23F) 550/sInelastic scattering

4He(24F,23F) 470/sneutron-knockout

4He(25Ne,23F) 1200/stwo-proton knockout


Summary and outlook• Discovery of new isotopes 40Mg, 42Al, 43Al, 44Si at NSCL• In-beam gamma-ray spectroscopy with fast beams

– Enables further scientific reach through luminosity gains of 100-1000 for a given driver accelerator

– Has in past decade transitioned into a worldwide effort with a set of robust experimental techniques that have contributed to many discoveries

• As new powerful drivers have come into operation in Japan, are under construction in Europe, and are being considered in United States (→ Prof. Tribble J4-4 Wed) this field will gain 1-2 orders of scientific reach from new detectors such as GRETA and AGATA

•

GRETA, I.Y. Lee, Lawrence Berkeley Lab GRETINA in front of S800 www.nscl.msu.edu/isf


Collaborators

P. Adricha), N. Aoic), D. Bazina), M. D. Bowena,b), B. A. Browna,b), C. Campbella,b),J. M. Cooka,b), D.-C. Dincaa,b), A. Gadea,b), M. Horoid), S. Kannoe), K. Kemperk), T. Motobayashic), A. Obertellia), T. Otsukaa,c,h), L. A. Rileyf), H. Sagawag), H. Sakuraic), K. Starostaa,b), H. Suzukih), S. Takeuchic), J. R. Terrya,b), J. Tostevini), Y. Utsunoij), D. Weisshaara), K. Yonedac), H. Zwahlena,b)

a) National Superconducting Cyclotron Laboratory, Michigan State Universityb) Department of Physics and Astronomy, Michigan State Universityc) RIKEN Nishina Center for Accelerator-Based Scienced) Physics Department, Central Michigan Universitye) Department of Physics, Rikkyo Universityf) Department of Physics and Astronomy, Ursinus Collegeg) Center for Mathematical Sciences, University of Aizuh) Department of Physics, University of Tokyoi) Department of Physics, University of Surreyj) Japan Atomic Energy Research Institutek) Physics Department, Florida State University

Documents

Examples of nuclear structure observables with fast beams Discovery of new isotopes