We report on γ-ray spectroscopy of low-lying excited states in the neutron-rich Kr94,95,96 isotopes measured as part of the "Shell Evolution And Search for Two-plus energies At RIBF"(SEASTAR) campaign at the RIKEN Radioactive Isotope Beam Factory. Excited yrast and non-yrast states were observed, and half-lives extracted via geant4 simulations. In Kr94,96 candidates for the 31- state were identified. For Kr95, the prompt SEASTAR data were combined with delayed spectroscopic data measured with the EURICA array to observe transitions on top of the known (7/2)+ isomer at a level energy of 195.5(3) keV. The comparison of the new experimental results with five-dimensional collective Hamiltonian (5DCH) and mapped interacting boson model (IBM) calculations, both using the Gogny D1M interaction, could suggest oblate-prolate shape coexistence already in Kr96.
Bibliographical noteFunding Information:
This work is supported by the Deutsche Forschungsgemeinschaft (DFG—German Research Foundation) under Grant No. BL 1513/1-1 and by the BMBF under Grants No. 05P15PKFNA, No. 05P19PKFNA, No. 05P15RDFN1, No. 05P19RDFN1, and No. 05P21RDFN1. We thank the RIKEN Nishina Centre accelerator staff and the BigRIPS team for providing the stable and high-intensity uranium beam and secondary beams, and the STFC (UK). J.P.E. thanks D. Regnier for useful discussions. The work of K. Nomura was supported by the Tenure Track Pilot Programme of the Croatian Science Foundation, the École Polytechnique Fédérale de Lausanne, and Project No. TTP-2018-07-3554, Exotic Nuclear Structure and Dynamics, with funds of the Croatian-Swiss Research Programme. B.D. and Z.L. were supported by the National Natural Science Foundation of China (Grants No. 12135004, No. 11635003, and No. 11961141004). R.T. was supported by JSPS Grant-in-Aid for JSPS Research Fellows JP14J08718.
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