A fully microscopic model of total level density in spherical nuclei

TL;DR

This paper introduces a comprehensive microscopic model for nuclear level density in spherical nuclei, integrating pairing, collective vibrations, and thermodynamics without fitting parameters, validated on nickel and zirconium isotopes.

Contribution

It presents the first microscopic model confirming the dominance of quadrupole and octupole vibrational enhancements in nuclear level density calculations.

Findings

Vibrational enhancement mainly due to quadrupole and octupole excitations.

Model accurately predicts thermodynamic quantities like excitation energy and entropy.

No fitting parameters used in the microscopic calculations.

Abstract

A fully microscopic model for the description of nuclear level density (NLD) in spherical nuclei is proposed. The model is derived by combining the partition function of the exact pairing solution plus the independent-particle model at finite temperature (EP+IPM) with that obtained by using the collective vibrational states calculated from the self-consistent Hartree-Fock mean field with MSk3 interaction plus the exact pairing and random-phases approximation (SC-HFEPRPA). Two important factors are taken into account in a fully microscopic way, namely the spin cut-off and vibrational enhancement factors are, respectively, calculated using the statistical thermodynamics and partition function of the SC-HFEPRPA without any fitting parameters. The numerical test for two spherical $^{60}$Ni and $^{90}$Zr nuclei shows that the collective vibrational enhancement is mostly dominated by the quadrupole and octupole excitations. This is the first microscopic model confirming such an effect, which was phenomenologically predicted long time ago and widely employed in several NLD models. In addition, the influence of collective vibrational enhancement on nuclear thermodynamic quantities such as excitation energy, specific heat capacity and entropy is also studied by using the proposed model.