Different isotopic composition as a signature for different processes leading to fragment production in midperipheral 58Ni+58Ni collisions at 30 MeV/nucleon

We report on the results of experiments performed to investigate the 58Ni+58Ni 30 MeV/nucleon reaction. In midperipheral collisions a massive fragment (4≤Z≤12) production has been observed. The emission patterns exhibit features consistent with dynamical fragmentation of a neck zone between the interacting nuclei, while in addition and at the same time, the projectile-like and target-like residues are subject to statistical decay. The nature of the fragments produced via the two different mechanisms differ both for what concerns charge distribution and isotopic composition. In particular, neutron rich fragments can be produced in dynamical processes, even if the starting nuclear matter presents a N/Z ratio close to the unity