Effect of projectile ground state spin on fission fragment anisotropies in B-10, B-11+Th-232 reactions

Fission fragment angular distributions have been measured for B-10(spin=3(+)), B-11(spin=3/2(-))+Th-232 reactions at projectile energies below and above the Coulomb barrier. The fragment anisotropies for the B-11 +Th-232 system are found to be significantly larger than the statistical saddle point model (SSPM) predictions at sub-barrier energies, while for the B-10+Th-232 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.