High-spin excitations of ~(81,82,83,85)Se: Competing single-particle and collective structures around N = 50

摘要

The ~(81,82,83,85) Se nuclei have been produced as fission fragments in the fusion reaction ~(18)0 + ~(208)Pb at 85 MeV bombarding energy and studied with the Euroball IV array. Their high-spin level schemes have been built from the triple γ-ray coincidence data and γ-γ angular correlations have been analyzed in order to assign spin and parity values to many observed states. The lowest-spin states of the two-neutron and three-neutron configurations are strongly mixed with two-proton excitations among the fp orbits. On the other hand, the highest-spin states of these neutron configurations are found to remain almost pure. Neutron excitation across the N = 50 gap is observed both in ~(83)Se_(49) and in ~(85)Se_(51).