Configuration of RISING for Measurements of Spin-alignment

and g-factors by TDPAD

50

82

50

82

Regions of Interest

prod. rates = 100-200 pps

prod. rates = 200-300 pps

prod. rates = 300-400 pps

prod. rates = 400-500 pps

prod. rates = 500-600 pps

prod. rates = 600-700 pps122Ag 123Ag 124Ag 125Ag 126Ag 127Ag 128Ag

123Cd 124Cd 125Cd 126Cd 127Cd 128Cd

A~130 region

U+Pb at 750 AMeV, 108 ppsFRS, GSI

129Cd 130Cd

124In 125In 126In 127In 128In 129In 130In 131In 132In 133In 134In

125Sn 126Sn 127Sn 128Sn 129Sn 130Sn 131Sn 132Sn 133Sn 134Sn

126Sb 127Sb 128Sb 129Sb 130Sb 131Sb 132Sb 133Sb 134Sb 135Sb 136Sb

prod. rates = 0-100 pps

127Te 128Te 129Te 130Te 131Te 132Te 133Te 134Te 135Te 136Te 137Te 138Te

128I 129I 130I 131I 132I 133I 134I 135I 136I 137I 138I 139I 140I 141I

129Xe 130Xe 131Xe 132Xe 133Xe 134Xe 135Xe 136Xe 137Xe 138Xe 139Xe 140Xe 141Xe 142Xe 143Xe 144Xe 141Xe

82

80

90

50

isomer observed at GSI

no isomer observed

Isotope Production

Spin-alignment

• Spontaneous fission - almost complete oblate alignment initially

BUT loss of alignment during de-excitation

Alignment ~ 0.28 for low-lying levels

• Preservation of alignment

(i) fully-stripped fragments (a) high primary beam energy

GSI not GANIL

(b) production target not too thick

(ii) Low (~ 20%) electron pick-up probability - depends on A and Z

high secondary beam energy > 150 MeV/u

(iii) implant into appropriate (thick) crystal, e.g. Pb

• Bruker B-E 25v Electromagnet

- Pole diameter 250 mm

- Total weight 1850 kg

- Excellent homogeneity

< 10-4 under typical conditions

TDPAD Set-up: Plan View

Air gap/mm

Maximum field/T

10 2.2

50 1.5

100 1.1

150 0.8

TDPAD Set-up: Side View

0.0 0.1 0.2 0.3 0.4 0.50.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fra

ctio

na

l unc

ert

ain

ty/%

Crystal-detector distance/m

B2

g

TDPAD Method

• Observe Larmor precession of nuclear spins via

2 2 2

2 2 2

3( , ) ( , / 2)( , ) cos[2( )]

( , ) ( , / 2) 4 L

A B QI t I tR t t

I t I t A B Q

• Sensitivity depends on

(i) Radiation parameter A2

(ii) Total number of emitted γ-rays

(iii) Number of detectors

(iv) Intrinsic efficiency of detectors

(v) Detector dimensions

(vi) Crystal-detector distances

Prompt Background

• Prompt flash

(i) shield detectors against low-energy photons

(ii) observe high-energy γ-rays in experiments

(iii) discard spin rotation data for t < 0.5 μs

(a) lose a lot of statistics

(b) isomers having t1/2 0.5 μs difficult to access

Summary

• 500 MeV/u 238U 150 MeV/u 135Te

22% probability of electron pick-up in thin plastic scintillator

22% of nuclei not aligned

reduced amplitude of oscillations in spin rotation pattern

greater statistics required

• higher energies excluded because of prompt flash and crystal thickness

• lower energies excluded because of increased probability of pick-up

BUT existing production cross-section based on 750 MeV/u 238U

-what is the production cross-section at 500 MeV/u?

• In A ~ 80 region, electron pick-up less probable

90 MeV/u acceptable prompt flash less severe

• The region A 140 may be completely excluded

Outstanding Issues

• Support structure for stopped beam campaign

• Support for magnet

• Installation and testing of magnet

- starting no earlier than July 2004

• Map of stray magnetic field

• Immunity of Cluster detectors to magnetic field

- insertion of detectors between coils of magnet possible?

• Require collaborators with experience in

(i) conducting isomer experiments

(ii) tuning FRS

(iii) operating data acquisition system

• Other groups invited to use our set-up