Fission fragment angular distributions for the systemsN14+Th232andB11+U235at near and sub-barrier energies

Abstract

Fission fragment angular distributions have been measured for the systems $^{11}\mathrm{B}+^{235}\mathrm{U}$ and $^{14}\mathrm{N}+^{232}\mathrm{Th}$, at sub and near-barrier energies. Complete and incomplete momentum transfer fission components have been separated around $90\ifmmode^\circ\else\textdegree\fi{}\phantom{\rule{0.3em}{0ex}}\text{c.m.}$ for $^{14}\mathrm{N}+^{232}\mathrm{Th}$. The contribution of incomplete momentum transfer events is found to be about $8%$ over the present energy range of investigation. In the $^{14}\mathrm{N}+^{232}\mathrm{Th}$ case, anisotropy data are found to be anomalous throughout the energy range, where as corresponding data for $^{11}\mathrm{B}+^{235}\mathrm{U}$ are found to be normal, with respect to the saddle-point statistical model predictions. The large ground state spin values of $^{11}\mathrm{B}$ and $^{235}\mathrm{U}$ are found to play a major role at the sub-barrier region in influencing the anisotropy values.