Fast fission: a dissipative mechanism following sometimes fusion

We discuss the conditions under which the fusion of two heavy ions is possible. We describe the results of a dynamical model for dissipative heavy ion collisions which shows that a fused trajectory can lead either to a compound nucleus, or to fast fission. This latter process is a mechanism which is intermediate between compound nucleus formation and deep inelastic reactions. The conditions under which fast fission occurs are discussed in details. The results of the model are compared with experimental data suggesting the existence of fast fission