Shape evolution in neutron-rich krypton isotopes beyond N=60; First spectroscopy of Kr

Flavigny, F.*; Doornenbal, P.*; Obertelli, A.*; Delaroche, J.-P.*; Girod, M.*; Libert, J.*; Rodriguez, T. R.*; Authelet, G.*; Baba, Hidetada*; Calvet, D.*; Chteau, F.*; Chen, S.*; Corsi, A.*; Delbart, A.*; Gheller, J.-M.*; Giganon, A.*; Gillibert, A.*; Lapoux, V.*; Motobayashi, Toru*; Niikura, Megumi*; Paul, N.*; Rouss, J.-Y.*; Sakurai, H.*; Santamaria, C.*; Steppenbeck, D.*; Taniuchi, R.*; Uesaka, T.*; Ando, T.*; Arici, T.*; Blazhev, A.*; Browne, F.*; Bruce, A.*; Carroll, R.*; Chung, L. X.*; Corts, M. L.*; Dewald, M.*; Ding, B.*; Franchoo, S.*; Grska, M.*; Gottardo, A.*; Jungclaus, A.*; Lee, J.*; Lettmann, M.*; Linh, B. D.*; Liu, J.*; Liu, Z.*; Lizarazo, C.*; Momiyama, S.*; Moschner, K.*; Nagamine, S.*; Nakatsuka, Noritsugu*; Nita, C.*; Nobs, C.*; Olivier, L.*; Orlandi, R.  ; Patel, Z.*; Podolyk, Zs.*; Rudigier, M.*; Saito, T.*; Shand, C.*; Sderstrm, P. A.*; Stefan, I.*; Vaquero, V.*; Werner, V.*; Wimmer, K.*; Xu, Z.*

The first -ray spectroscopy of very neutron rich Kr isotopes was carried out at the RIBF at RIKEN Nishina center. Excited states in these isotopes were populated via (p,2p) reactions using radioactive Rb beams accelerated to 220 MeV/nucleon. The new data show a significant increase in deformation beyond N=60, as well as competing configurations (shape-coexistence) at low energy. The data were compared with beyond-mean-field calculations which predict level energies in good agreement with observation, and suggest oblate-prolate shape coexistence.