Level densities and thermodynamical properties of Pt and Au isotopes

TL;DR

This study measures nuclear level densities of Pt and Au isotopes below the neutron separation energy, revealing constant-temperature behavior, pairing effects, and insights into single-particle level space.

Contribution

It provides new experimental data on level densities of specific isotopes and characterizes their thermodynamical properties, including pairing effects and entropy differences.

Findings

Level densities follow the constant-temperature model.

Isotopes share the same temperature above the pairing threshold.

Sequential peaks indicate nucleon Cooper pair breaking.

Abstract

The nuclear level densities of $^{194-196}$Pt and $^{197,198}$Au below the neutron separation energy have been measured using transfer and scattering reactions. All the level density distributions follow the constant-temperature description. Each group of isotopes is characterized by the same temperature above the energy threshold corresponding to the breaking of the first Cooper pair. A constant entropy excess $\Delta S=1.9$ and $1.1$ $k_B$ is observed in $^{195}$Pt and $^{198}$Au with respect to $^{196}$Pt and $^{197}$Au, respectively, giving information on the available single-particle level space for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is revealed by sequential peaks in the microcanonical caloric curve.