Effect of projectile ground state spin on fission fragment anisotropies in10B,11B+232Threactions

Abstract

Fission fragment angular distributions have been measured for 10 B(spin53 1 ), 11 B(spin53/2 2 )1 232 Th reactions at projectile energies below and above the Coulomb barrier. The fragment anisotropies for the 11 B 1 232 Th system are found to be significantly larger than the statistical saddle point model ~SSPM! predictions at sub-barrier energies, while for the 10 B1 232 Th system the deviations from SSPM predictions are found to be much less. The present results indicate that the ground state spin of the projectile influences the fragment anisotropies at sub-barrier energies in a larger way than predicted by the statistical model with the inclusion of the M-state distributions. Calculations were carried out based on the entrance channel dependent K-states distribution and preequilibrium fission models, with inclusion of ground state spin of the projectiles, which are found to explain the variation of fission fragment anisotropies as a function of bombarding energy for both the systems.