Role of thermal fluctuations in the damping of the giant dipole resonance of spherical and deformed nuclei: 90Zr and 164Er

Abstract

We study the damping width of the giant dipole resonance (GDR) built on the ground state and on excited states of 90Zr, which is spherical at zero spin and temperature, and 164Er which is deformed. Neither of these nuclei changes appreciably their equilibrium shape when excited. Nonetheless, fluctuations due to finite temperature produce a marked increase in the width of the GDR of 90Zr, leaving essentially unchanged that of 164Er. This is because in the case of deformed nuclei thermal fluctuations imply the sampling of both larger and smaller deformations around the equilibrium shape, while spherical nuclei can only feel larger distortions. In spite of the stability of the GDR of 164Er, the angular distribution of the associated γ-rays is strongly affected by the temperature.