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

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 2

Region of interest

Z=48 Cd

132Sn

Z=50Z=50 Sn

N=82

122,123,124,126,128Cdr p

roce

ss

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 3

Neutron-rich Cd isotopes

*T. R. Rodríguez et al., Phys. Lett. B668, 410 (2008)

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.govW. Watanabe et al., PRL 111, 152501 (2013)

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 4

Experimental set-up

MINIBALL

DSSSD

MINIBALL

Beams fromREX-ISOLDE

@ 2.85 MeV/u

“Safe” Coulomb excitation• Gamma – particle coincidences• Isobaric beam contaminants

• 24 6-fold segmented HPGe detectors ( ≈ 7%)• fully digital electronicsN. Warr et al., EPJ A 49, 40 (2013)

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 5

Prompt -ray spectra

NEW

Analysis of 128Cd/128In: Sabine Bönig (PhD thesis, TU Darmstadt, 2014)

• 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

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 6

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 | 7

Maximum likelihood fit

Lifetime measurement with DSAM

• find optimal M20-M22 combination• if available, additional information like lifetimes is included• projection of 1 contour on axes

Michael Thürauf (Master thesis, TU Darmstadt)

without

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 8

New beyond mean field calc‘s

Beyond mean field including triaxiality• prolate deformation ( ≈ 0)• excitation energies better reproduced• large overlap of wave functions ... large B(E2)Tomás Rodriguez (TU Darmstadt)

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 9

Collectivity in even Cd isotopes

122,124,126CdS. Ilieva et al., PRC 89, 014313 (2014)

• 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 | 10

123Cd – first odd Cd isotope

DC wrt projectileDC wrt target recoil

• Coulomb excitation of both 123Cd and 123mCd• Level scheme of 123Cd well known in literature ...???

Anna-Lena Hartig (Master thesis, TU Darmstadt, 2014)

(unr

esol

ved

mul

tiple

t)

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 11

123Cd – revised level scheme

466

412

222

598

Excitation energy of isomer:

144 keV (not 316 keV)A. Kankainen et al., PRC 87, 024307 (2013)

Matrix elements, e.g.117 keV: 0.92 eb376 keV: 0.50 eb... similar size

376

117

Inconsistencies with literature H. Huck et al., PRC 40, 1384 (1989)

... revised level scheme (... mainly single-step excitations!!!) - -ray yield following Coulomb excitation - coincidences ... very few - variation of 123Cd/123mCd content in beam (RILIS, only broad band laser available for this run)

1-6 June 2014 | ARIS 2014 - Tokyo | Institut für Kernphysik, TU Darmstadt | Thorsten Kröll | 12

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

and

than

k yo

u

for y

our a

tten

tion!!

!!