Preparation of an isomerically pure beamand future experiments

Outline

TAS Workshop, Caen, March 30-31, 2004

Klaus Blaum for the ISOLTRAP CollaborationCERN PH-IS Geneva and GSI Darmstadt

Motivation

Summary

Preparation of an isomerically pure beam

Experimental setup and procedure

Future experiments

Motivation: The identification puzzle in 70Cu

(1+) 0 44.5(2)

(3-) 101.1(3) 33(2)

(6-) 242.4(3) 6.6(2)

J E / keV T1/2 / s

IT5%

IT50%

–95%

–50%

–=100%Mass excess Lit:-63202(15) keV

Ground and isomericstates of 70Cu

Problems / unknown parameters:- number of isomeric states- spin assignement- order of states- mass excess value of ground state

Requirements:- clear state to mass assignement- high selectivity- high efficiency- ultra-high resolving power

Solution:Combination of laser resonance ionization, -decay spectroscopy andPenning trap mass spectrometry

1. Surface Ionization Ion Source:

No isobaric selectivity, limited applicability

2. Plasma Ion Source (ECR-Source):

No isobaric selectivity

3. Resonance Ionization Laser Ion Source (RILIS):

High isobaric selectivity by resonant laser ionization

Limitation by surface ionized isobars

Resonance Ionization Laser Ion Source (RILIS)

Example: Cupper excitation scheme

Principle of Penning Traps

Cyclotron frequency: Bm

qfc

2

1B

q/m

B

q/m PENNING trap Strong homogeneous

magnetic field

Weak electric 3D

quadrupole field

z0

r0

ring electrode

end cap

Frans Michel Penning

Hans G.Dehmelt

Ion Motion in a Penning Trap

Motion of an ion is the superposition of three characteristic harmonic motions:– axial motion (frequency fz)– magnetron motion (frequency f–)– modified cyclotron motion (frequency f+)

The frequencies of the radial motions obey the relation

c-+ fff

magnetron motion (f-)

modified cyclotronmotion (f+)

axial motion (fz)

zr

r-

r+

Typical frequenciesq = e, m = 100 u,B = 6 T

f- ≈ 1 kHzf+ ≈ 1 MHz

Excitation of Radial Ion Motions

Dipolar azimuthal excitationEither of the ion's radial motions can be excited

by use of an electric dipole field in resonancewith the motion (RF excitation)

amplitude of motion increases without bounds

Quadrupolar azimuthal excitationIf the two radial motions are excited at their

sum frequency, they are coupled

they are continuously converted into each other

+Ud -Ud

r

r0

U

-Uq

-Uq

r0

r

+Uq+Uq

Conversion of radial motions

Magnetron excitation: Cyclotron excitation: +

TOF Resonance Mass SpectrometryS

can

of e

xcita

tion

freq

uenc

y

Quadrupolar radial excitation near fc

coupling of radial motions, conv.

Time-of-flight (TOF) measurement

Ejection along the magnetic field lines

radial energy converted to axial energy

Dipolar radial excitation at f-

increase of r-

MCPDetector

1.2

m

Time-of-flight resonance technique

Resolving power: excexc= TfR

1071195 1071200 1071205 1071210 1071215 1071220 1071225

200

220

240

260

280

300

320

340

Measurement Theoretical Fit

85Rb

Tim

e-of

-flig

ht [

s]

Excitation frequency [Hz]

Me

an

tim

e o

f flig

ht

/ s

Excitation frequency frf / Hz

T1/2 =

TOF Cyclotron Resonance Curve (Stable Nuclide)

Determine atomic mass from frequency ratio with a well-known reference massDetermine atomic mass from frequency ratio with a well-known reference mass

TOF as a function of the excitation frequency

Bmq

πf

21

=c

Centroid:

TOF Cyclotron Resonance Curve (Radionuclide)

0 1 2 3 4 5 6 7 8 9240

270

300

330

360

390

63Ga T1/2 = 32.4 s

Mea

n tim

e of

flig

ht /

s

Excitation frequency RF

- 1445125 / Hz

Determine atomic mass from frequency ratio with a well-known reference massDetermine atomic mass from frequency ratio with a well-known reference mass

TOF as a function of the excitation frequency

Bmq

πf

21

=c

Centroid:

frf

Triple-Trap Mass Spectrometer ISOLTRAP

ISOLDEbeam (DC)

HV platform

RFQ structure

MCP 5

precisionPenningtrap

coolingPenningtrap

carbon clusterion source

2.8-keV ionbunches

laser beam

MCP 3

MCP 1

60 keV

stable alkaliion referencesource

C60 pellet

80

100

120

140

160

180

200

220 32ArM

ean

TOF

(s

)

RF 2842679 (Hz)-40 -30 -20 -10 0 10

G. Bollen, et al., NIM A 368, 675 (1996)F. Herfurth, et al., NIM A 469, 264 (2001)

cluster ion source

preparation Penning trap

precision Penning trap

stable alkali ionreference source

ion beam cooler and buncher

removal of contaminant ions

(R = 105)

determination of cyclotron frequency

(R = 107)

B = 4.7 T

B = 5.9 T

Nd:YAG 532 nm

1.2

m

10 cm

K. Blaum et al., EPJ A 15, 245 (2002)

10 cm

ISOLTRAP Setup

1 m

Isomer Separation

Isomerism in 68Cu:

1+

6-

1+

240

270

300

330

360

390

240

270

300

330

360

390

260

280

300

320

340

360

380

400

me

an

TO

F (

us)

fexc - 1338940 (Hz)

0 5 10 15 20 25 30 35

6

as producedby ISOLDE

isolation of the 1+ ground state

isolation of the 6- isomeric state

Resolving power of excitation: R ≈ 107

Population inversion of nuclear states Preparation of an isomerically pure beam

0+

1+

721.6 keV6-

g: T1/2 = 31.1 sm:T1/2 = 3.75 min

IT 84%

16%

100%68Cu

68Zn

K. Blaum et al., Europhys. Lett., submitted (2004).

Solving the Identification Puzzle in 70Cu

(6-) 0 44.5(2)

(3-) 101.1(3) 33(2)

(1+) 242.4(3) 6.6(2)

I E / keV T1/2 / s

IT5%

IT50%

–95%

–50%

–=100%Mass excess Lit:-63202(15) keV

Isomerism in 70Cu: Hyperfine structure of 70Cu isomers (using laser ionization):

16%

4%

80%

(spectrum provided by U. Köster)

Intensity ratio:

normalized to the area

J. Van Roosbroeck et al., Phys. Rev. Lett. 92, 112501 (2004).

270

300

330

360

390

Mea

n T

OF

/

s

Identification of Triple Isomerism in 70Cu

270

300

330

360

390

Mea

n T

OF

/

s

0 2 4 6 8 10 12

270

300

330

360

390

Mea

n T

OF

/

s

c - 1300610 / Hz

16%

4%

80%

Intensity ratio:

normalized to the area

with cleaning of 6– state

Unambiguous state assignment!c = B

qm

(6–) state = gs

(3–) state = 1.is

1+ state = 2.isR 1·107

Preparation of an isomerically pure beam!

ME of ground state is 240 keV higher than literature value!

Excellent agreement with decay studies.

101(3) keV101(3) keV

242(3) keV242(3) keV

New Detector Setup

Drift tube

Window (open access)

Channeltrondetector

Spare MCP detectorFeed-through

MCPDetector

Ions from the precision trap

Open Detector Geometry

DeTech ChanneltronDeTech Channeltron

+

e-

Principle of a CDEMPrinciple of a CDEM

-2.5 kV

-5 kV

Typical gain at 2.5 kV: ~5107 Dark noise: ~20 mHz (measured) Pulse width / Dead time: ~25 ns (measured) Rinse time: ~5 ns (measured) Detection efficiency (low energy ions): >90%

Typical gain at 2.5 kV: ~5107 Dark noise: ~20 mHz (measured) Pulse width / Dead time: ~25 ns (measured) Rinse time: ~5 ns (measured) Detection efficiency (low energy ions): >90%

Beta-Counter and Tape Station

(Courtesy W. Geithner)

Isomericallypure ion beam

Tape station

Tape stationavailable at GSI!

Beta-counter

Applications

Help, advice and good ideas are welcome!

Identification of unknown contaminations

Collection of isomerically pure samples

Background-free decay studies

Background-free half-life measurements

Preliminary studies of further applications,e.g. post-acceleration with REX-ISOLDE

Identification of unknown contaminations

Collection of isomerically pure samples

Background-free decay studies

Background-free half-life measurements

Preliminary studies of further applications,e.g. post-acceleration with REX-ISOLDEBUT: Number of ions at present limited

to about 10 ions/proton pulse.

Conclusion and Outlook

• ISOLTRAP can perform high-precision mass measurements

(< 10-8) on very short-lived nuclides (< 100 ms) that are

produced with very low yields (< 100 ions/s)

• ISOLTRAP can prepare isomerically pure beams and demonstrated population inversion of nuclear states

• Isomerically pure beams open a new area in low-energy nuclear physics research

• Setup of a tape station, decay spectroscopy and half-life measurements on an isomerically pure beam are planned within the next few years

Thanks to my co-workers:G. Audi, G. Bollen, D. Beck, P. Delahaye, C. Guénaut, F. Herfurth,

A. Kellerbauer, H.-J. Kluge, D. Lunney, D. Rodríguez, C. Scheiden-berger, S. Schwarz, L. Schweikhard, G. Sikler, C. Weber,

C. Yazidjian ..., and the ISOLTRAP and ISOLDE collaboration

Thanks for the funding and support:GSI, BMBF, CERN, ISOLDE,

EU networks EUROTRAPS, EXOTRAPS, and NIPNET

Thanks a lot foryour attention.

Not to Forget …

New Detector Setup

Drift tube

Feedthrough

Spare MCP detector

Channeltrondetector

Window (open access)

Ions from precision trap

MCPDetector

0.0 4.0x105 8.0x105 1.2x106 1.6x106 2.0x106

44

46

48

50

144

148

152

156

= (24.6 ± 1.3) ns

= (27.2 ± 1.9) ns

40Ca /

44Ca

40Ca /

42Ca

Isot

open

verh

ältn

is

40Ca Zählrate / s40Ca Zählrate [Hz]

Iso

tope

rat

io

40Ca count rate / Hz

Dead time measurementDead time measurement

: dead time R: isotope rationA: count rate

= = (R-R0)/nA

1-R0

1 - slope

axis section

Typical gain at 2.5 kV: ~5107

Dark noise: ~20 mHz (measured)

Pulse width / Dead time: ~25 ns (measured)

Rinse time: ~5 ns (measured)

Detection efficiency (low energy ions): >90%

Typical gain at 2.5 kV: ~5107

Dark noise: ~20 mHz (measured)

Pulse width / Dead time: ~25 ns (measured)

Rinse time: ~5 ns (measured)

Detection efficiency (low energy ions): >90%

Specification of the CDEM