Transport theory and doorway configuration in dissipative heavy-ion collisions

Abstract

The evolution of the collision complex can be divided roughly into three stages: mutual approach of the nuclei, local equilibration and slow relaxation of macroscopic degrees of freedom. The last stage has been extensively studied within the framework of transport theories. The main steps in the derivation and application of a Fokker-Planck equation for the slowly varying macroscopic (collective) variables are discussed. Mass transfer and dissipation of relative angular momentum are well described by the theory. In order to bridge the gap between the initial stage and the third stage an explicitly time-dependent dynamical potential in the relative motion is introduced. This potential is due to the initial correlations which arise from the ground-state configurations of the approaching nuclei. The generalized Fokker-Planck equation is applied to compound-nucleus formation and dissipative collisions. The possible existence and some characteristic features of a long-living component of dissipative collisions are studied.