Georgi Georgiev CSNSM, Orsay, France Nuclear structure studies at the r-process path Coulomb excitation of odd-A neutron-rich Rb isotopes at REX-ISOLDE.

Overview Physics motivation – sudden onset of deformation in the neutron-rich N=60 region Experimental approach Radioactive beams (post-accelerated) Coulomb excitation – few general remarks The Coulex setup at REX-ISOLDE Experimental results: 93 Rb and 95 Rb spherical features below N=60 97 Rb and 99 Rb – a sudden onset of deformation right above N=60 Summary and outlook

N=60 - from spherical to strongly deformed structures S. Naimi et al., PRL 105, (2010) Ground States Kr (Z=36)  NO onset of deformation Mass and laser measurements show that the Kr isotopes do not undergo a rapid shape change of their ground states from N=58 to 60 Zr (Z=40) and Sr (Z=38)  clear shape change across N=60 9/2 + [404], 1/2 - [550], 3/2 - [541], 3/2 + [411] W. Urban et al., Eur. Phys. J. A22, 241 (2004)‏

What is going on with the proton side? Rb’s (Z = 37) r-process path – according to one of the scenarios it can pass exactly through the 93,95,97,99 Rb nuclei  3/2 - [312],  3/2 - [301],  3/2 + [431] C. Thibault et al., Phys. Rev. C23, 2720 (1981) Rb's ground states  Study of the excited states in the Rb isotopes from below (Coulomb excitation) – a key for the understanding of the nuclear structure around N=60

1.4 GeV protons from PS-Booster keV X 1+  GPS or HRS REX trap cooling and bunching EBIS charge breeding to A/q ~ 4 REX up to 3 MeV/u MINIBALL 8 triple Ge clusters 6-fold segmented

Coulomb excitation – few remarks K. Alder et al., RMP 28 (56) 432 Coulomb excitation – purely electromagnetic interaction involved – full analytical description

Miniball setup beam dump Ge detector Particle detection Ionization chamber Beam from 2.9 MeV/u    CD Detector (16° – 53°) REX beam Reaction Chamber & Miniball cluster array Secondary target 1-2 mg/cm 2

93,95,97, 99 Rb – excited states known before Isomeric decays  - decay 

Experimental results 93,95 Rb – work in progress! Strong resemblance between the level schemes (and transition probabilities) in 93 Rb and 95 Rb

Experimental results 97,99 Rb – work in progress! “All new” excited states in 97 Rb and 99 Rb A “collaps” of the structure after N=60 Considerable contamination for 99 Rb (50 ms) from products decaying in-flight Still to be done before B(E2) could be extracted: angular distribution of gamma-rays for spin-determination existence of gamma-gamma coincidences ?

The Coulomb-excitation is a powerful tool for nuclear structure studies far from stability giving independent and complementary information to the other approaches The structure of the Rubidium isotopes is one of the keys ingredients needed to clarify the nature of the sudden onset of deformation around the neutron-rich N=60 region, giving an insight to the possible proton involvements into the process. A considerable number of levels populated by the Coulomb excitation in the supposedly spherical 93 Rb and 95 Rb – a starting point for the understanding of the deformed to 97 Rb and 99 Rb. First unambiguous identification of excited states in 97 Rb and 99 Rb. Additional experimental sensitivity (e.g. polarized beams?) needed for the very exotic cases where no much experimental information is available. Summary and outlook

Collaboration CSNSM, Orsay, France - C. Sotty LPSC, Grenoble, France – G.S. Simpson CEA/DIF/DPTA/SPN, Arpajon, France - J.M. Daugas, R. Chevrier, P. Morel IKP Köln, Germany - A. Blazhev, K. Geibel, P. Reiter, M. Seidlitz, B. Siebeck, N. Warr IKS, Leuven, Belgium - N. Bree, J. Diriken, B. Lannoo University of Camerino, Italy - S. Das Gupta University of Liverpool, UK - L. Gaffney Warsaw University, Poland - K. Hadynska-Klek, P. Napiorkowski, M. Zielinska TU Darmstadt, Germany - T. Kroell, M. Scheck ISOLDE, CERN, Geneva, Switzerland - J. Pakarinen, F. Wenander ANU, Canberra, Australia - A. Stuchbery and REX-ISOLDE and Miniball collaborations

99 Rb – pushing the limits β -decay 99 Rb case T 1/2 = 50 ms; trapping time ~80 ms; breading time ~80 ms Shift of components Different T 1/2 Simulation trying to reproduce IC Ionization Chamber

Experiment vs. theory

Mean-field theory results for odd-mass Rb’s R. Rodriguez-Guzman, P. Sarriguren, L. M. Robledo, PRC82, R (2010) A<89 – spherical 91,93,95 Rb – oblate plus shape coexistence A>99 – strongly prolate deformed

93 Rb preliminary results 93 Rb on MeV/u : 93 Rb (T 1/2 = 5.8 s) 6 E 6 pps (2 E 7/µCu) G. S. Simpson et al. Phys. Rev. C 82, (2010) γ- transition 253 keV 266 keV 324 keV 734 keV 913 keV 1332 keV type 5/2 -  3;5/2 - 5/2 -  1;3;5/2 - 5/2 -  3;5/2 - 5/2 -  (7;9/2 - ) 5/2 -  (7/2 - ) target excitation

95 Rb preliminary results 95 Rb on MeV/u : 95 Rb on MeV/u : γ- transition 236 keV 254 keV 342 keV 392 keV 619 keV 934 keV 1171 keV 1332 keV type unknown 5/2 -  (7/2 - ) unknown target excitation (Sn) target excitation (Ni) 95 Rb (T 1/2 = 377 ms) 1 E 6 pps (3 E 6/µCu) G. S. Simpson Phys. Rev. C 82, (2010)

97 Rb preliminary results 97 Rb on MeV/u : known transitions unknown transitions target excitation contaminants ( 97 Sr, 97 Y …) MeV/u : 97 Rb on MeV/u :type unknown 97 Sr unknown target excitation (Pt) γ- transition 68 keV 103 keV 124 keV 167 keV 191 keV 227 keV 241 keV 356 keV First observation of excited states in 97 Rb 97 Rb (T 1/2 = 170 ms) 5 E 5 pps (4 E 5/µCu)

99 Rb preliminary results 99 Rb on MeV/u : known transitions unknown transition target excitation contaminants ( 99 Sr, 99 Y …) γ- transition energy type 68 keVunknown 90 keV 99 Sr 107 keV 99 Sr, 99 Y 117 keVcontaminant 124 keV 99 Sr, 99 Y 161 keV 99 Sr, 99 Y 192 keV 99 Y 215 keV 99 Sr 294 keVcontaminant 356 keVtarget excitation (Pt) 99 Rb (T 1/2 = 50 ms) few E 3 pps First observation of excited state in 99 Rb 99 Rb on MeV/u :