Transcript Quadrupole collectivity in neutron

Quadrupole collectivity in
neutron-rich Cd isotopes
Thorsten Kröll
for the IS411/IS477/IS524 collaborations
Work supported by BMBF (Nr. 06DA9036I and 05P12RDCIA), EU through
EURONS (No. 506065) and ENSAR (No. 262010), HIC for FAIR, and the MINIBALL/REX-ISOLDE
Region of interest
N=82
132Sn
Z=50 Sn
Z=50

Z=48 Cd
122,123,124,126,128Cd
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 2
Neutron-rich Cd isotopes
E(2+) drops from 126Cd to 128Cd!
Not reproduced by SM
Beyond Mean Field* approach with
• Gogny D1S force
• angular momentum projection
• particle number projection
• configuration mixing (GCM)

• trend of E(2+) reproduced
• E(2+) somewhat too large
128Cd
is prolate deformed!?!
Data: nndc.bnl.gov
W. Watanabe et al., PRL 111, 152501 (2013)
*T. R. Rodríguez et al., Phys. Lett. B668, 410 (2008)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 3
Experimental set-up
MINIBALL
Beams from
REX-ISOLDE
@ 2.85 MeV/u
MINIBALL
DSSSD
“Safe” Coulomb excitation
• Gamma – particle coincidences
• Isobaric beam contaminants
• 24 6-fold segmented
HPGe detectors (e ≈ 7%)
• fully digital electronics
N. Warr et al., EPJ A 49, 40 (2013)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 4
Prompt g-ray spectra
• 646 keV is indeed the 2+  0+ transition in 128Cd!!!
• Coulomb excitation of isobaric In contamination
- level scheme of 126In needs revision A. Scherillo et al., PRC 70, 054318 (2004)
- new SM calculations agree with finding (G. Simpson, UWoS)
- conversion electron measurement (August 2013 @ ILL) ... analysis ongoing
Analysis of 128Cd/128In: Sabine Bönig (PhD thesis, TU Darmstadt, 2014)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 5
Analysis procedure
• “safe” Coulomb excitation ... single step dominates
• reorientation effect .... quadrupole moments
2+
0+
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 6
Maximum likelihood fit
• find optimal M20-M22 combination
• if available, additional information like lifetimes is included
• projection of 1s contour on axes
without t
Lifetime measurement with DSAM
Michael Thürauf (Master thesis, TU Darmstadt)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 7
New beyond mean field calc‘s
Tomás Rodriguez (TU Darmstadt)
Beyond mean field including triaxiality
• prolate deformation (g ≈ 0)
• excitation energies better reproduced
• large overlap of wave functions
... large B(E2)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 8
Collectivity in even Cd isotopes
122,124,126Cd
S. Ilieva et al., PRC 89, 014313 (2014)
u
p
p
• experimental B(E2) value for 128Cd robust (different conditions in analysis)
• general trend for even Cd isotopes continued
- larger B(E2)’s than SM prediction
- B(E2)’s well reproduced by BMF
- very limited sensitivity to Q2
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 9
123Cd
– first odd Cd isotope
• Coulomb excitation of both 123Cd and 123mCd
• Level scheme of 123Cd well known in literature ...???
DC wrt projectile
DC wrt target recoil
Anna-Lena Hartig (Master thesis, TU Darmstadt, 2014)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 10
123Cd
– revised level scheme
Inconsistencies with literature H. Huck et al., PRC 40, 1384 (1989)
... revised level scheme (... mainly single-step excitations!!!)
- g-ray yield following Coulomb excitation
- gg coincidences ... very few
- variation of 123Cd/123mCd content in beam (RILIS, only broad band laser
available for this run)
Matrix elements, e.g.
117 keV: 0.92 eb
222
376 keV: 0.50 eb
... similar size
598
412
466
117
376
Excitation energy
of isomer:
144 keV (not 316 keV)
A. Kankainen et al., PRC 87, 024307 (2013)
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 11
Summary and Outlook
• Safe Coulomb excitation of even neutron-rich isotopes 122,124,126,128Cd
... B(E2) values are larger than predictions from large scale SM calculations
... better agreement with BMF ... axially symmetric shapes
... no clear conclusion from Q2(2+) values ... small deformation preferred
• First successful run with odd isotope 123Cd
... level scheme needs revision ... new decay experiment desirable
... both positive and negative parity orbitals seem to contribute similarly
to collectivity
• Continuation of programme at HIE-ISOLDE
... multiple Coulomb excitation
... lifetime measurements with plunger
... 130Cd (... worth a try at HIE-ISOLDE?)
... narrow band laser to ionise selectively g.s. or 11/2- isomer in odd isotopes
... transfer reactions to pin down single-particle properties
1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 12