Heavy-ion friction force from a gas-kinetic model

A friction force is derived from the two-body collisions of projectile nucleons with target nucleons in the overlap region of their densities. The diffuse surfaces of the heavy ions are treated as Fermi gases. A certain average of the resulting friction force turns out to be identical in structure with the phenomenological Tsang-Swiatecki linear force. In this approach, the strength coefficient of the latter force can be calculated from the free two-nucleon scattering cross section without adjustable parameters. A strength is obtained which agrees well with the value found by Siwek-Wilczynska and Wilczynski from an empirical fit. (Auth.)