Symmetric mass fragmentation following capture in reactions of 4.8--8 MeV/nucleon /sup 208/Pb on /sup 50/Ti, /sup 52/Cr, /sup 58/Fe, and /sup 64/Ni using the fusion model based on the dynamical fragmentation theory

As a first application of our fusion model, the dynamical fragmentation process of fusion and subsequent fission is analyzed in the reactions of 4.8--8 MeV/nucleon /sup 208/Pb on /sup 50/Ti, /sup 52/Cr, /sup 58/Fe, and /sup 64/Ni. In this two step model, the colliding nuclei are first shown to be captured in the pockets behind the adiabatic interaction barriers and then the composite systems so formed, being strongly excited, fission adiabatically. The calculated capture cross sections agree reasonably well with the experiments and the mass distributions are systematically symmetric, independent of the choice of relative separation distance R and the large structure in the cranking masses. The symmetric mass fragmentation is a (dynamical) liquid drop effect and the peaks or other detailed structure in mass distributions depend on how the temperature would modify the masses and also on the dynamical coupling of mass asymmetry with the relative motion. This demands refined measurements of the fission data for larger mass asymmetry. The calculated critical angular momentum, which refers to the vanishing of the interaction barrier, in these reactions occurs at the incident energy greater than 8 MeV/nucleon. This suggests a possible importance of extending these experiments beyond their present energy limits