Quantal and Thermal Dampings of Giant Dipole Resonances in90Zr,120Sn, and208Pb

The damping of the giant dipole resonance (GDR) is studied in ${}^{90}\mathrm{Zr}$, ${}^{120}\mathrm{Sn}$, and ${}^{208}\mathrm{Pb}$ as a function of temperature $T$. The results show that the coupling of GDR to the $\mathrm{pp}$ and $\mathrm{hh}$ states is responsible for the increase of the GDR width with increasing $T$ up to 3 MeV and its saturation at higher $T$. The quantal width, caused by the coupling to $\mathrm{ph}$ excitations, decreases slowly with increasing $T$. An overall agreement is found between the theoretical evaluations and the recent experimental data in heavy-ion fusion reactions and inelastic $\alpha$ scattering. At very high $T$ a behavior similar to the transition from zero to ordinary sounds is observed.