why are we (in general) interested in q?

First combined DSAM and Coulex experiment at REX-ISOLDE – measuring the sign of the spectroscopic quadrupole moment of the 21

+ state in neutron-rich 140Ba *

8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer

Christopher Bauer1, Jörg Leske1, Thorsten Kröll1, Norbert Pietralla1, Vinzenz Bildstein2, Roman Gernhäuser2, Reiner Krücken2, Rudi Lutter3,

Chavdar Stoyanov4, Dimitar Tarpanov4

1Institut fur Kernphysik, TU Darmstadt, 64289 Darmstadt 2Physik-Department E12, TU Munchen, 85748 Garching 3Maier-Leibnitz-Laboratorium, LMU Munchen, 85748 Garching 4Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria

*supported by theBMBF (06 DA 9040 I) and HIC for FAIR

Why are we (in general) interested in Q?

Q describes the deviation of the charge distribution from spherical symmetry in a nucleus

The intrinsic quadrupole moment Q0 (in the reference frame of the nucleus) is related to the deformation parameter β by

The observable is the spectroscopic quadrupole moment Q, which is related to Q0 in the case of the first 2+ state by


The diagonal matrix element

The matrix elements are evaluated from measured yields / cross-sections in comparison with Coulomb excitation calculations


2+

0+

M20

M22

The idea


With new lifetime informationthe situation changes dramatically

ExperimentMINIBALL at REX-ISOLDE (IS411)


CD detector

MINIBALL

γ

θγ

γ

θp

RIB140Ba

96Mo

Z=50

N=

82

Barium (Z=56)

140Ba

132Sn

Ebeam = 392 MeV

Target: 1mg/cm2 96Mo

DSAM analysis

Additional run

natCu target(thickness: 1mm)

140Ba is stopped


Time difference [µs]

Energy [keV]

raw spectrum

backgroundsubtracted

602 keV

602 keV

DSAM analysis: Fit


The DSAM fit was done by J. Leske.

= 12.5(6) ps

20 individual fits for each MB Ge core in this experiment

weighted average

Coulex cross-section


The cross-section is sensitive on the

quadrupole moment!

The cross-section is sensitive on the

quadrupole moment!

SensitivityS = (Q+-Q-)/Q0

Complete statistics


The new determined lifetime fixes the M20

matrix element.

The new determined lifetime fixes the M20

matrix element.

Old lifetime: 14(6) psNew Lifetime: 12.5(6) ps

Splitted statistics


Comparison to theory

QPM: Q = 0.1(M22 = 0.13)

The quadrupole moment must be

positive!-> OBLATE SHAPE

The quadrupole moment must be

positive!-> OBLATE SHAPE

e-

Recoil-in-vacuum

15.4.2010 | MINIBALL Workshop Leuven | IKP Darmstadt | Christopher Bauer

Ion beam

(140,142Ba)

96Mo

(0.9mg/cm2)

Ion beam

(140,142Ba)

natCu (892mg/cm2)

I

I

J

F

γ

γ

Angular Distributions

Thick target: natCu 142Ba, distribution for 360 keV line ( )


g factor

Limit for g ( ) in 140Ba is |g|≤0.38 RIV method is applicable But need appropriate calibration isotope(s)


Summary

Results

140Ba Coulex evaluation Lifetime:

= 14(6) ps 12.5(6) ps21(9) W.u. 18.8(9) W.u.

Qspec > 0 oblate shape

RIV method First time tested at REX-ISOLDE Limit for g( )-factor in 140Ba

|g|≤0.38

Conclusions

Both methods are complementary to standard MINIBALL experiments Need extra run with suitable

thicker target for DSAM

Need extra runs for distribution without deorientation and with calibration isotope(s)g factor

Be aware of contamination!


Thank you for your attention!

Thank you for your attention!

why are we (in general) interested in q?

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