FROM BINARY FISSION TO MULTIFRAGMENTATION IN THE DECAY OF HEAVY EXCITED NUCLEI

The decay modes of heavy excited nuclei formed in dissipative collisions for the systems Ar+Au at 60 MeV/u and Kr+Au at 43 MeV/u are studied. A transition from binary fission towards multi-fragment emission is observed around 3 MeV/u excitation energy, independently of the considered system. The charge distributions of the three target-emitted fragments suggest a smooth change from ''fission'' events (as a ''natural'' continuity of binary fission) to ''residue production'' then to ''symmetric ternary fragmentation'' events when the excitation energy increases from 3 MeV/u to 5 MeV/u.