Multipole excitations in hot nuclei within the finite temperature quasiparticle random phase approximation framework

TL;DR

This study investigates how finite temperature affects nuclear excitations in $^{68}$Ni and $^{120}$Sn using a self-consistent quasiparticle random phase approximation, revealing new low-energy modes and modifications to existing resonances.

Contribution

It provides a detailed analysis of temperature-induced changes in nuclear excitation spectra within a fully self-consistent framework using Skyrme interactions.

Findings

Emergence of low-energy excitations from thermally occupied states.

Weak impact of temperature on the isovector giant dipole resonance.

Temperature effects lead to decreased centroid energies and quenched collectivity in quadrupole states.

Abstract

The effect of temperature on the evolution of the isovector dipole and isoscalar quadrupole excitations in $^{68}$Ni and $^{120}$Sn nuclei is studied within the fully self-consistent finite temperature quasiparticle random phase approximation framework, based on the Skyrme-type SLy5 energy density functional. The new low-energy excitations emerge due to the transitions from thermally occupied states to the discretized continuum at finite temperatures, whereas the isovector giant dipole resonance is not strongly impacted by the increase of temperature. The radiative dipole strength at low-energies is also investigated for the $^{122}$Sn nucleus, becoming compatible with the available experimental data when the temperature is included. In addition, both the isoscalar giant quadrupole resonance and low-energy quadrupole states are sensitive to the temperature effect: while the centroid energies decrease in the case of the isoscalar giant quadrupole resonance, the collectivity of the first $2^{+}$ state is quenched and the opening of new excitation channels fragments the low-energy strength at finite temperatures.