Microscopic Nuclear Level Densities from Fe to Ge by the Shell Model Monte Carlo Method

Abstract

We calculate microscopically total and parity-projected level densities for $\beta$-stable even-even nuclei between Fe and Ge, using the shell model Monte Carlo methods in the complete $(pf+0g_{9/2})$-shell. A single-particle level density parameter $a$ and backshift parameter $\Delta$ are extracted by fitting the calculated densities to a backshifted Bethe formula, and their systematics are studied across the region. Shell effects are observed in $\Delta$ for nuclei with Z=28 or N=28 and in the behavior of $A/a$ as a function of the number of neutrons. We find a significant parity-dependence of the level densities for nuclei with $A\text{alt}60$, which diminishes as $A$ increases.

Comments: to be published in Phys. Lett. B; includes 5 eps figures