Surface response in the Fermi-liquid drop and nuclear transport properties

Response functions for isoscalar multipole excitations are calculated for a large range of temperatures and analyzed in terms of transport coefficients. The dynamics of the nucleons is treated semiclassically by applying the collisional Landau-Vlasov equation for the interior region, supplemented by the ‘‘effective nuclear surface approximation’’ introduced previously to describe the dynamics of the surface. Collisions are considered in modified relaxation time approximation with a temperature- and frequency-dependent relaxation time. The strength distribution shows a marked transition from the zero sound like behavior at small temperatures to the one corresponding to collision dominated modes. The latter appear at small frequencies and are underdamped. Within our present model the transition occurs at large temperatures of about T≥4 MeV. For the intermediate temperatures the overdamped modes are found as related to the low-lying peaks in the strength function. The results are illustrated by the calculations of the strength function for the quadrupole excitations in the nucleus ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.