Level densities and thermodynamical properties of Pt and Au isotopes

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.