Stability of the N=50 shell gap in the neutron-rich Rb, Br, Se, and Ge isotones

Abstract

The low- and medium-spin states of the N=50 neutron-rich, Rb-87(37), Br-85(35), Se-84(34) and Ge-82(32) isotones have been populated in deep-inelastic processes produced by the interaction of 460 MeV Se-82 ions with a Os-192 target. The subsequent gamma decay has been investigated at the Laboratori Nazionali di Legnaro using the GASP gamma-ray detector array. The comparison of the experimentally observed excited states with shell-model calculations performed with and without neutron degrees of freedom has allowed the investigation of the role of the neutron-core breaking excitations and therefore of the N=50 shell gap. The inclusion of neutron configurations in the shell-model calculations results in an improved agreement between the experimental and calculated level energies at medium and high spin. These results highlight the considerable contribution of neutron-core particle-hole excitations across the N=50 shell gap to the level configurations. The overall agreement of the measured excited states with the shell-model predictions is indicative of the persistence of the N=50 shell gap down to Z=32.

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