Nuclear level densities away from line of ${\hat{I}}^2$-stability

Abstract

The variation of total nuclear level densities (NLDs) and level density parameters with proton number $(Z)$ are studied around the ${\hat{I}}^2$-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 microsopic 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.

Accepted in Journal of Physics G: Nuclear and Particle Physics