Interpretation of fission fragment anisotropies in the fission of ²³⁸U induced by intermediate energy ⁴He ions

Abstract

The fragment anisotropy data in the fission of ²³⁸U induced by 23-115 MeV ⁴He ions are analyzed taking into consideration the expected differences in the fragment anisotropies of the fissions following compound nucleus and direct interactions. The present analysis supports the theoretical prediction made earlier that the transition state seen by the fissioning nucleus shifts from the second barrier at low energies to the liquid drop model saddle point at higher excitation energies. However, the determination of the excitation energy where the liquid drop model transition state is encountered depends on the assumption regarding the reaction mechanism and the anisotropy for the direct interaction fission component. The need for experimental measurements of the fragment anisotropies of both the direct interaction fission and compound nucleus fission components is pointed out.