'Fast fusion' and 'quasifission': Two possible mass-relaxation modes in asymmetric heavy-ion collisions leading to systems with Ztot=108

The qualitative differences between the experimental mass distributions observed in the collisions 32S (192 MeV) + 238U and 40Ar (220 MeV) + 232Th leading to the same compound system Ztot=108 are explained within a simple diffusion model. It is demonstrated that there generally exist two different modes of the mass relaxation process. In the ''fast fusion'' channel the massasymmetry increases rapidly, whereas in the 'quasifission' process the system drives slowly towards symmetry. The relative contributions of both channels to the cross section depend sensitively on the position of the injection point in the driving potential. (orig.)