Study of the fragmentation process in central collisions for the systems Pb + Au and Pb + Ag

Numerous works experimental as well as theoretical were carried out in the last years for achieving a better understanding of different de-excitation modes of the massive systems, and particularly, of the fragmentation processes. For these systems the multifragmentation is more often considered as subsequent to the formation of exotic structures of bubble or torus types. The collisions between very heavy nuclei can not result in stable residue and consequently are the most adequate for the study of the multifragmentation at relatively low energies. In this work the fragmentation processes of systems obtained in central Pb + Au and Pb + Ag reactions are compared within the Landau-Vlasov model. The influence of isospin, Coulomb and mass effects on the formation of bubble or toroid like configurations is studied