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

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