Particle exchange as the dissipative mechanism in nucleus-nucleus collisions

We discuss a model where the colliding nuclei are treated as two Germi gases which exchange particles, momentum and entropy through a window in the mean single particle potential. Even at zero temperature transfer of particles is possible because phase space which is not Pauli blocked is available due to unequal Fermi distributions on either side of the window. The difference comes about by a possible mismatch of the mean velocities, of the chemical potentials and of the temperatures. Based on this picture we discuss in a unified manner a variety of dissipative phenomena like mass drift, thermal feed back on the mass drift, partition of excitation energy, energy and angular momentum dissipation, and fluctuations in the relative momentum and mass number. (orig.)