Fission fragment angular distributions: A probe to study heavy-ion fusion dynamics

It is shown that when fusion is initiated at relatively larger distances due to the presence of rotational couplings, the Businaro-Gallone barrier shifts towards higher mass asymmetry, thus favoring further mass equilibration towards symmetric configurations. This leads to the occurrence of preequilibrium fission events for all systems which affect the fission fragment angular distributions at subbarrier energies. The fission fragment angular distributions calculated as an admixture of compound nuclear and preequilibrium components explains quite well the energy dependence of the angular anisotropies for many systems around the actinide regions irrespective of the entrance channel mass asymmetries at energies both well below and above the Coulomb barrier. From the fits to the angular distributions, K-equilibration time is deduced to be $\sim 6\times {10}^{-20}$ s for a temperature $\sim 1\mathrm{MeV}.$