Shell-model study of the N = 49 isotones

Abstract

The N = 49 isotones 88Y, 89Zr, 90Nb, 91Mo, 92Tc and 93Ru are studied in the framework of the shell model with valence nucleons occupying the 2p1 2 and 1g9 2 single-particle levels. The residual proton-neutron effective interaction is determined by a least-squares fit to the experimental energies of states in these nuclei with well established spins and parities. We examine the effects of requiring the effective interaction to conserve seniority and model-space isospin. It is found that the existing body of experimental data is consistent with conservation of T = 1 seniority but that the data call for small isospin mixing that can be traced to modelspace truncation effects. The resulting shell-model wave functions are used to calculate energy levels, single-nucleon spectroscopic factors and electromagnetic transition rates. These model wave functions also provide a basis for a qualitative discussion of the weak coupling multiplet structure that persists in the low-lying states of all of these nuclei. In general, all observed properties of yrast levels and analog states are well reproduced by our model as are the positions of many non-yrast levels. Within this model space unique 0+ anti-analog states emerge in 88Y, 90Nb and 92Tc, but the 9 2+ and 1 2- anti-analogs are highly fragmented in the even-Z nuclei. © 1976.