Nuclear level densities away from line of β-stability

Abstract

The variation of total nuclear level densities (NLDs) and level density parameters with proton number (Z) are studied around the β-stable isotope, Z 0, for a given mass number. We perform our analysis for a mass range A = 40 to 180 using the NLDs from popularly used databases obtained with the single-particle energies from two different microscopic mass-models. These NLDs which include microscopic structural effects such as collective enhancement, pairing and shell corrections, do not exhibit inverted parabolic trend with a strong peak at Z 0 as predicted earlier. We also compute the NLDs using the single-particle energies from macroscopic-microscopic mass-model. Once the collective and pairing effects are ignored, the inverted parabolic trends of NLDs and the corresponding level density parameters become somewhat visible. Nevertheless, the factor that governs the (Z - Z 0) dependence of the level density parameter, leading to the inverted parabolic trend, is found to be smaller by an order of magnitude. We further find that the (Z - Z 0) dependence of NLDs is quite sensitive to the shell effects.