Shell model study of the high spin states in the N=50 isotones 92Mo, 93Tc, 94Ru, and 95Rh.

Abstract

The low lying levels in N=50 isotones have been well described within the shell model framework. These calculations were performed assuming an inert neutron core and the valence protons occupying either the (${\mathit{p}}_{1/2}$,${\mathit{g}}_{9/2}$) or (${\mathit{f}}_{5/2}$,${\mathit{p}}_{3/2}$,${\mathit{p}}_{1/2}$,${\mathit{g}}_{9/2}$) orbits. With the advent of multidetector arrays the level schemes of these nuclei have been extended to high spin regimes (J=20-25\ensuremath{\Elzxh}). The inclusion of neutron core excitation (neutron particle-hole excitation across the N=50 shell gap) was essential to adequately describe these observed higher angular momentum states. Calculations involving neutron particle-hole excitation across the N=50 shell gap, coupled to the lower valence proton configurations, were not feasible due to computational limitations. This paper describes a truncation scheme devised to perform large basis shell model calculations. The level sequences observed in the N=50 isotones $^{92}\mathrm{Mo}$, $^{93}\mathrm{Tc}$, $^{94}\mathrm{Ru}$, and $^{95}\mathrm{Rh}$ are interpreted on the basis of the shell model calculations in the configuration space ${\mathit{f}}_{5/2}$, ${\mathit{p}}_{3/2}$, ${\mathit{p}}_{1/2}$, ${\mathit{g}}_{9/2}$ for the protons and ${\mathit{p}}_{1/2}$, ${\mathit{g}}_{9/2}$, ${\mathit{g}}_{7/2}$, ${\mathit{d}}_{5/2}$, ${\mathit{d}}_{3/2}$, ${\mathit{s}}_{1/2}$ for the neutrons. The excitation of a ${\mathit{g}}_{9/2}$ neutron across the N=50 shell, into the next major oscillator shell describes the observed higher angular momentum states in these nuclei.