Gamma-ray spectroscopy and shell model description of high spin states in B-stable 91,92 Zr.

Identification of near-yrast states in the stable 91,92Zr isotopes has been carried out using the fusion evaporation reactions 82Se(13C,xn)95-xZr at an incident beam energy of 50 MeV from the Yale ESTU tandem accelerator. Gamma-ray spectroscopy of more than fifty previously unreported states up to ~ 20h and to excitation energies of more than 13 MeV are identified for the first time above the previously observed tau= 6 mus, Ipi = 21/2+ isomer in 91Zr. Angular Correlation and Linear Polarisation analyses were performed on these transitions. Ten new transitions were also observed in 92Zr. A modified effective interaction has been produced for the shell model code OXBASH which embeds the empirical matrix elements of the Ji-Wildenthal eta50j interaction into a new interaction developed by Hjorth-Jenson for N=50 nuclei. This interaction together with newly derived single particle energies allows calculations in the basis pi[1f5/2, 2p3/2, 2p1/2, (lg9/2)], nu[2p1/2,1d9/2, 2d5/2, 3s1/2, 1g7/2,1h11/2] limited only by the matrix sizes possible with the code. Results from the calculations performed aided in the assignment of spin and parity to the lower lying yrast levels above the Ipi = 21/2+isomer which were shown to result from the alignment of a single neutron in the nuh11/2 orbit coupled to two maximally aligned protons in g9/2