LABORATORI NAZIONALI DI LEGNARO
The mass distributions observed in heavy-ion induced fission are invariably of symmetric shape and single peaked because the compound nucleus is generally formed with larger excitation energy well above barrier. The fragment shell effects observed in the mass distributions in the case of light ion induced reaction are not seen in the case of heavy-ion induced reactions. We have carried out measurements for a number of systems over a wide range of excitation energies to study mass and energy correlations. We have also studied the angular anisotropy as a function of mass. A systematic analysis of the mass variance reveals that sA2 increases exponentially with the compound nucleus temperature and different bans corresponding to different fissility are observed and mass variance calculated at a fixed temperature increases with fissilility. However when sA2 is calculated for a fixed temperature of the fission fragments, the variation of sA2 with temperature falls on a single global curve and the fissility dependence is washed out. These results suggest that mass distribution of the fission fragment is decided at a later stage of the saddle to scission transition and scission configuration plays an important role in deciding the mass and total kinetic energy distribution of the fragments.

DATA: 01-10-2004