Study of mass asymmetry effect in the entrance channel for deep inelastic collisions between heavy ions

The reactions (52Cr+56Fe) and (16O+92Mo) were studied extensively to learn about the influence of the mass asymmetry of the entrance channel on Deep Inelastic Collisions (DIC). These two systems have very different entrance channel asymmetry but both of them lead to the same ensemble of nucleons. The incident energies were choosen to be 265 MeV for Cr and 187 MeV for O so that the maximum angular momentum is the same in both the cases. The experimental results of the quasi-symmetric system (Cr+Fe) show that a large number of fragments have the characteristic properties of fission fragments. However, comparison of these results with those of an asymmetric system (O+Mo), forming the same compound nucleus with higher excitation energy, leads to think that these events can not be accounted for fission. It has been shown that these events could be considered as DIC products. The distributions of different multidifferential observables were reproduced with the help of a diffusion model, and with the condition of introducing a notion of half life time of the composite system. The half-life, thus calculated, seems to vary as a function of mass asymmetry of the entrance channel: 20.10-22S for the system Cr+Fe, 2.10-22S for the system O+Mo and 10.10-22S for a third system 20Ca+64Ni which has an intermediate mass asymmetry. Further it seems that the evaporation residue cross section in symmetric systems is far less than what we can expect from classical calculations