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, Z0, 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 Z0 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-Z0) 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-Z0) dependence of NLDs is quite sensitive to the shell effects.

Indispensability of cross-shell contributions in neutron resonance spacing

“…Nuclear level densities (NLDs) are one of the key ingredients for studying nuclear reactions [1], particularly the astrophysical reaction rates at a fixed temperature in terms of the Maxwellian average of cross-sections over a wide energy range [2][3][4][5][6]. NLDs have been calculated using many different approaches, such as simple phenomenological models based on non-interacting degenerate Fermi gas [7][8][9][10] and semi-classical models [11,12] to more complex microscopic mean-field models [13][14][15]. The collective effects are included through the rotational and vibrational enhancement factors in these models.…”