Temperature Dependence of the Width of the Giant Dipole Resonance in120Sn and208Pb

The giant-dipole resonance (GDR) in ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ is studied as a function of excitation energy, angular momentum, and intrinsic width. Theoretical evaluations of the full width at half maximum (FWHM) for the GDR strength function are compared with recent experimental data and are found to be in overall agreement. Differences observed between ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ are attributed to strong shell corrections in ${}^{208}\mathrm{Pb}$ favoring spherical shapes at low temperatures. At high temperature, the FWHM in ${}^{120}\mathrm{Sn}$ exhibits effects due to the evaporation width of the compound nucleus.