Main trends in heavy ion reaction mechanisms when the energy increases

The influence of collision terms on the dynamical processes leads to very important changes in the aspects of heavy ion reactions when the energy per nucleon increases from a few MeV/n up to some 45 MeV/n. For peripheral collisions the deep inelastic reactions are replaced by a slightly inelastic fast perturbation. Quasi-elastic phenomena are still observed with a few nucleon transfer reaction towards unbound states. For central collisions, fusion processes still persist but the transfer of linear momentum is limited due to a direct emission of fast light particles. Therefore, very high energy deposits are produced and very hot nuclei are formed which decay by statistical deexcitation. Residual nuclei and fission fragments are the final products up to a certain excitation energy. But limits are reached, at an excitation energy of the order of 4-5 MeV per nucleon -which is slightly higher for light systemps than for heavy ones- where the fusion process is not followed subsequently by the usual decay. Possibly a multifragmentation mechanism is the new way by which a very excited piece of nuclear matter disrupts very rapidly. Finally, in addition to peripheral and central collisions, it seems that collisions at intermediate impact parameters are responsible for the creation of a hot transient species made of the projectile plus a piece of the target, which, because of its high temperature, very promptly explodes into several light fragments and alpha-particles