Formation and decay of hot nuclei in heavy ion collisions

The properties of the multifragmentation of "hot sources" produced in the C a-40 + Ca-40 reaction have been studied at a beam energy 35 MeV/nucleon. Tw o signatures of prompt multifragmentation, which make use of special featur es of particle emission from the "freeze out volume", together with an anal ysis of the reduced relative velocity between pairs of intermediate mass fr agments, indicate the presence of a transition from sequential decay to pro mpt multifragmentation at an excitation energy of about 3 MeV/nucleon.