Magnetic moment measurements with the high-velocitytransient field (HVTF) technique at relativistic energies

Andrea JungclausIEM-CSIC

Madrid, Spain

Andrew StuchberyAustralian National University

Canberra, Australia

Instituto de Estructura de la Materia – Consejo Superior de Investigaciones Científicas

Jörg LeskeTU Darmstadt

Darmstadt, Germany

Why to measure magnetic moments ofshort-lived excited states in exotic nuclei ?

One example …

D.C. Radford et al., Phys. Rev. Lett. 88 (2002) 222501

Te

B(E2) anomaly in 136Te

136Te

N. Benczer-Koller et al., PLB 664(2008)241

Exp. and theoretical g(2+) in Te the isotopes

136Te

g-factor is very sensitive to relative proton(neutron) composition of nuclear wavefunction !

How to measure magnetic moments ?

/g = N/ħ·B·teff

Larmor frequency

Time integral measurement of theprecession angle

L = g · N/ħ · B

kT fields required for short teff (<) !

Fermi contact field at the nucleus:

B1s = 16.7 Z3 R(Z) [T]

R(Z) 1+(Z/84)2.5 relativistic correction factor

for 1s electrons

Magnetic fields of this strength in general available at thenucleus ONLY due to its own electrons !

randomly oriented electron spins: attenuation of -ray angular distribution

“nuclear deorientation”

oriented electron spins (polarization): precession of -ray angular distribution

“transient fields”

Fer

mi c

onta

ct f

ield

[T

esla

]

H O F Ne Mg Si Xe

MTesla !

kTesla !

Three different techniques to measure g-factorsof short-lived states using radioactive beams

nuclear deorientation132Te @ Oak Ridge 3.0 MeV/u

N.J. Stone, A.E. Stuchbery et al.,Phys. Rev. Lett. 94 (2005) 192501

38,40S @ MSU 40 MeV/uA.D. Davies et al., PRL 96 (2006) 112503

A.E. Stuchbery et al., PRC 74 (2006) 054307

42,44,46Ar @ MSU & N=40 Fe @ MSUOctober 2008 SP: A.E. Stuchbery

72Zn @ GANIL 60 MeV/uApril 2008 SP: G. Georgiev, A. Jungclaus

high-velocity transient fieldlow-velocity transient field

138Xe @ REX-ISOLDE 2.8 MeV/u2006/2009 SP: A. Jungclaus, J. Leske

132Te @ Oak Ridge 3.0 MeV/uN. Benczer-Koller et al., PLB 664(2008)241

Only very few experiments so far advantages and disadvantagesof the different techniques still need to be explored !

Nothing yet at relativistic energies !

Transient fields: From the low- to the high-velocity regime

Transient field strength in Fe host

low-energyCoulex

intermediate-energy& relativistic Coulex

v/c3-7%

maximum around v=Z∙v0

strength scales with Z3 (Z2 in Gd)

ξ1s: degree of polarization of 1s electronsF1

1s: ion fraction with unpaired 1s electronsB1s: Fermi contact field of 1s electrons

Z∙v0: 1s electron velocity

v/c20-50%

A.E. Stuchbery et al.,Phys. Rev. C74 (2006) 054307Phys. Lett. B611 (2005) 81

Problem:Transient field strength studiedonly up to Sulfur (in Canberra).What happens for higher Z ?

Btf (v, Z) = ξ1s(v, Z) · F11s(v, Z) · B1s(Z)

30 shifts of parasitic 136Xe beam approved by GSI PAC in 2009 calibration of TF strength in the 132Sn region !

0.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

30 60 90 120 150

-2

0

2

30 60 90 120 150

-2

0

2

134Te

134Xe

angle (deg)

Wla

b(

)S

nu

c(

), S

2 N

How to measure the precession of a -rayangular correlation with the PRESPEC setup ?

136Xe primary beam @ 500 MeV/u2.5 g/cm2 Be target

100 MeV/u

62 MeV/u

400 mg/cm2 Gd

83.5 MeV/u

4.1 ps

=3.0(2) ps2.3 ps

134Xe

Full simulation performed using thecode GKINT by A. Stuchbery

figure of merit

teff = 1.4 ps, v/Zv0 = 1.07-0.93

/g = 129 mrad, Bave = 1.9 kTesla

Including decay:

N=7500 photopeak counts per field per day inClusters A, D and E

LYCCA-01.5º

2.1º

0.1º-1.7º

Geometry of the PRESPEC Ge array

134Te

P

E

DA

J N

5 10 15 20 25 30 35 40 450

50

100

150

200

250

300

350

angl

e (

deg)

angle (deg)

PRESPEC

10o 40o !

All Ge crystals in the range 40º and three pairsof Cluster detectors close to the horizontal plane !

B

From the RISING@GSI to the AGATA@GSI setup

In case of a successful calibration experiment with the RISING setup we wouldlike to tackle a first physics case in the 132Sn region with the AGATA@GSI setup !

standardconfiguration

C. Domingo

It is still under study whether a larger than the standarddistance would lead to a higher sensitivity to the precession.

Transient fields (TF) largestaround 1s electron velocity

Relativistic heavy ions “in principle”well suited for g(2+) measurements !

TF strength only known up to Z=16 (30)

We need at least one calibration pointto tackle the 132Sn region.

Approved parasitic beamtime at GSI !

Magnetic moment information isimportant (sometime E(2+) and

B(E2) is not sufficient) !

Summary & Conclusions

Once the TF strength is known real physicscases in the 132Sn region can be studied

with the AGATA@GSI setup !