Coulomb excitation of neutron-rich odd-A Cd isotopes

1. Coulomb excitation of neutron-rich odd-A Cd isotopes Thorsten Kröll* / Gary Simpson+ CERN-INTC-2011-040, INTC-P-306  *TU Darmstadt – +LPSC Grenoble – TU München –TRIUMF – LMU München KU Leuven– CERN–IEM CSIC Madrid–Univ. Sofia –IFIN HH Bucharest IRNRE BAS Sofia –HIL Warszawa –Univ. Köln –NSCL, MSU –Univ. Guelph Work supported by BMBF (Nr. 06DA9036I), LOEWE / HIC for FAIR, and the MINIBALL/REX-ISOLDE collaborations

2. IS477 – Quadrupole collectivity in 128Cd First Coulomb excitation of the neutron-rich isotope 128Cd (August 2011) • g-ray spectrum recorded with MINIBALL • Doppler correction with respect to projectile-like particles in coincidence • Laser ON / NO background subtraction 128Cd: 2+ → 0+ Preliminary Analysis by Sabine Bönig (PhD student, TUD) et al. November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 2

3. Collectivity in even Cd isotopes Exp. (IS411): nThomas Behrens (PhD, TU München) Shell model: pA. Scherillo et al., PRC 70, 054318 (2004) pG. Simpson (2011) pLoI for AGATA-Prespec@GSI (2010) … abandoned Beyond-mean-field (BMF): qA. Jungclaus, J.L. Egido et al. (2007) Modern large scale shell model calculations clearly underestimate B(E2) values!!!!! November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 3

4. Why to investigate odd Cd isotopes? • Even neutron-rich Cd isotopes • Considerably larger collectivity experimentally observed compared • to predictions by large scale shell model calculations • … some contributions to collective wave functions are missing • … surprise as the region is near to the doubly-magic 132Sn • Odd neutron-rich Cd isotopes • No B(E2) values known • Level scheme is „divided“ in two parts: • - positive parity states build on the (3/2+) ground state (nd3/2) • (none experimentally known for A>123) • - negative parity states build on the long-lived (11/2-) isomer (nh11/2) • … selectivity to contributions from particular single particle orbitals • ISOLDE beam contains both the ground state and the isomer • Proposed experiment profits from the unique capability of ISOLDE to • deliver also isomerically purified beams November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 4

5. 123Cd – current knowledge Ordering of levels is experimentally not confirmed November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 5

6. 125,127Cd – current knowledge Ordering of levels is experimentally not confirmed November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 6

7. Collectivity in odd Cd isotopes - SM t B(E2) » 8 W.u. or larger [e2b2] t t t t t t t t t t • Napoli interaction • - CD Bonn • - Vlow-k • 123Cd expected • to be even more • collective November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 7

8. Aims of the proposed experiment • Identify the collective 7/2- to 15/2- states (negative parity) above • the long-lived 11/2- isomer and clarify the level ordering • Identify collective states (positive parity) build on the ground state • Problem: • Assignment of previously unobserved g-rays è selective laser ionisation • Impact on interpretation: • Information on which single particle orbitals contribute to the collectivity • in the odd isotopes • - Supports the understanding of the collectivity in the neighbouring even • isotopes ... same configurations may contribute to collectivity • èComprehensive picture how nuclear structure evolves along the • Cd isotopic chain approaching N=82 November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 8

9. Successional experiments at HIE-ISOLDE Experiment at REX will already yield a data set rich of information • HIE-ISOLDE enables continuation of programme (LoI INTC-I-111 )employing … • Multiple Coulomb excitation • - Analysis needs some starting points • - Experiments have to be performed with different targets or beam energies • (… as already done now at REX!) • Particular case: • Coulomb excitation from the positive parity states to negative parity states • or vice versa… presumably via E3 • è decay path is not identitical with excitation path • Transfer experiments • Tagging of populated states by their characteristic decay g-rays • … which have to known November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 9

10. Rate estimate / beam request (I) • UCx production target, RILIS, 2.85 MeV/u (as in the 128Cd case) • Half-lifes of 123,125,127Cd are longer compared to 128Cd (T1/2 = 0.28 s) • … longer breeding time possible • Beam contaminations: • isobaric Cs, In (decay product of Cd) • Neutron converter or not??? Would increase yields by a factor of 5! • Can be decided only with yield check using actual ISOLDE target!!!! * * with neutron converter November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 10

11. IS477 – beam composition Under otherwise stable conditions the beam composition changed dramatically … ratio Cd/Cs by roughly a factor of 20!!!! 9:42 h 128Cs 5:45 h 128Cs 128Cd 128Cd • Proton beam on ISOLDE target (no converter) • Laser ON … lasers had been checked • Yield measurement confirmed disappearance of 128Cs contamination • … obviously the odd isotopes cannot be measured under conditions • like in the left spectrum! November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 11

12. Rate estimate / beam request (II) • Standard MINIBALL + CD set-up (T-REX possible), 64Zn target (1.5 mg/cm2) • Proton intensity 2 mA, eREX=5%, converter target • Isomeric ratio: 50% (has to be determined by characteristic decay g-rays) • è typically 30-60 particle-g-coincidences/h for 123Cd per excited level • B(E2) values with 5% statistical error within 2 days • è expected statistics lower by a factor of 10 for125Cd B(E2) values with 10% statistical error within 4 days • è127Cd currently remains only an option … • + 1 day for the laser scans (will benefit from the results of IS497) • + 1 day for beam preparation We request 24 shifts (8 days) of beam time November 3, 2011 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 12