DISSIPATION, POLARIZATION AND FLUCTUATION IN GRAZING HEAVY-ION COLLISIONS AND THE BOUNDARY TO THE CHAOTIC REGIME

The boundary between the grazing deep inelastic collisions and the quasi-fission or fusion reactions is studied though classical, semiclassical and WKB approximations. Although transfer reactions are responsible for the main part of the large energy loss in grazing collisions that come close to the barrier, the excitation energy is more than compensated by an additional attraction, due to polarization, so that the projectile reaches the barrier almost as if no reactions had taken place. At some distance outside the Coulomb barrier an instability occurs towards a merging of the surfaces, which also appears if no Coulomb barrier exists. Fluctuations in energy, partly due to transfer reactions, but mainly to the zero-point motion of the low-lying surface modes give an important spread in the capture angular momentum.