Excitation energy and angular momentum dependence of nuclear level densities and spin cut-off factor in SPA and SPA + RPA approaches

Abstract

We investigate the excitation energy ( E ∗ ) and angular momentum ( J) dependence of nuclear level density and spin cut-off factor (σ) within microscopic approaches based on SPA and its extension SPA + RPA representation of the grand partition function for quadrupole-quadrupole interaction model Hamiltonian. For 110Sn, we find that excitation energy dependence of the total level density obtained within these approaches is significantly different. On the other hand, these approaches yield similar behaviour for J-dependence of the level density at fixed values of E ∗ . Values of σ SPA + RPA at low E ∗ are found to be slightly smaller than σ SPA but they tend to become almost the same at higher E ∗ (> 30 MeV) . We also find that Bethe's formula for fixed- J level density based on the spin cut-off approximation can be used to compute ϱ(E ∗, J) near the yrast line provided one uses an appropriate value of the spin cut-off factor.