Nuclear level density and thermal properties of $^{115}$Sn from neutron evaporation

TL;DR

This study measures the nuclear level density of $^{115}$Sn using neutron evaporation spectra and compares it with various models, revealing the most accurate description and identifying a phase transition in thermal properties.

Contribution

The paper provides the first experimental measurement of $^{115}$Sn level density and compares it with multiple theoretical models, highlighting the EP+IPM as most accurate.

Findings

EP+IPM best matches experimental data

Identifies a transition in nuclear pairing from strong to weak

Provides thermal properties like entropy and temperature profiles

Abstract

The nuclear level density of $^{115}$Sn has been measured in an excitation energy range of $\sim $2 - 9 MeV using the experimental neutron evaporation spectra from the $^{115}$In($p,n$)$^{115}$Sn reaction. The experimental level densities were compared with the microscopic Hartree-Fock BCS (HFBCS), Hartree-Fock-Bogoliubov plus combinatorial (HFB+C), and an exact pairing plus independent particle model (EP+IPM) calculations. It is observed that the EP+IPM provides the most accurate description of the experimental data. The thermal properties (entropy and temperature) of $^{115}$Sn have been investigated from the measured level densities. The experimental temperature profile as well as the calculated heat capacity show distinct signatures of a transition from the strongly-paired nucleonic phase to the weakly paired one in this nucleus.