Nuclear structure and dynamics from heavy - ion induced fission reactions

Abstract

The study of heavy - ion fusion and fission reactions at near - barrier energies continues to be a rich source of information as regards nuclear structure and dynamics. From a comprehensive statistical model analysis of the fusion and the fission data including information on the pre - scission neutrons, for a large number of compound nuclei with masses around 200, it has been possible to determine reliably the fission barrier, the nuclear moment of inertia and the shell correction at the saddle point. Interestingly, it is found that for the nuclei in the mass region around 200, a significantly large fraction of the ground state shell correction persists at the deformed saddle - point. Systematic measurements of the fission fragment angular distributions spanning a range of projectiles with A = 9 to 19, bombarding the Th,U and Np targets have clearly brought out role of the entrance channel dynamics involving a new type of non - equilibrium fission, which we call pre - equilibrium fission comempeting with the equilibrium compound nucleus fission. A new model which takes into account the deformation and the spin values of the target and the projectile, the orientation and the entrance channel mass asymmetry dependence of the interacting nuclei has been developed which provides a good description of the fission fragment angular distribution data both at above and below barrier energies.