Why are we (in general) interested in Q?
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Transcript of 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
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
The diagonal matrix element
The matrix elements are evaluated from measured yields / cross-sections in comparison with Coulomb excitation calculations
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
2+
0+
M20
M22
The idea
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
With new lifetime informationthe situation changes dramatically
ExperimentMINIBALL at REX-ISOLDE (IS411)
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
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
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
Time difference [µs]
Energy [keV]
raw spectrum
backgroundsubtracted
602 keV
602 keV
DSAM analysis: Fit
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
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
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
The cross-section is sensitive on the
quadrupole moment!
The cross-section is sensitive on the
quadrupole moment!
SensitivityS = (Q+-Q-)/Q0
Complete statistics
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
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
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
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 ( )
15.4.2010 | MINIBALL Workshop Leuven | IKP Darmstadt | Christopher Bauer
g factor
Limit for g ( ) in 140Ba is |g|≤0.38 RIV method is applicable But need appropriate calibration isotope(s)
8.12.2010 | ISOLDE workshop | TU Darmstadt | Christopher Bauer
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!
15.4.2010 | MINIBALL Workshop Leuven | IKP Darmstadt | Christopher Bauer
Thank you for your attention!
Thank you for your attention!