Shell-model calculations for the energy levels of the N=50 isotones with A=80–87

Abstract

The detailed features of the calculated energy-level schemes and of the single-particle, orbit-occupancy properties of the low-lying levels of the N=50 isotones 80Zn, 81Ga, 82Ge, 83As, 84Se, 85Br, 86Kr, and 87Rb are presented and discussed. These results are obtained with a new effective Hamiltonian operator obtained empirically from an iterative fit to experimental energies taken from all experimentally studied (A=82–96) N=50 nuclei. The model space for the calculations consists of active 0f5/2, 1p3/2, 1p1/2, and 0g9/2 proton orbits relative to a nominal 78Ni core. This space is truncated internally by restricting the number of particles excited from the negative-parity orbits into the g9/2 orbit to be no greater than four. The typical structures predicted for these lighter N=50 isotones are found to be dominated by well-mixed combinations of fp-orbit configurations, with the g9/2 orbit playing a minor role in all but a few special cases. The model energy-level spectra are compared with existing experimental information, as are calculated spectroscopic factors for single-proton stripping and pickup reactions.