Fission dynamics study inAm243andFm254

Fission fragment mass distributions in the reactions $^{11}\mathrm{B}+\phantom{\rule{0.16em}{0ex}}^{232}\mathrm{Th}$ and $^{11}\mathrm{B}+\phantom{\rule{0.16em}{0ex}}^{243}\mathrm{Am}$ were measured in an energy range around the barrier. No sudden change in the width of the mass distribution as a function of center-of-mass energy was observed at near-barrier energies, indicating no quasifission transition in the near-barrier energies. Interestingly, the previous measurements of fission fragment angular anisotropies for the same systems showed significant departure from the statistical saddle-point model predictions at near-barrier energies, indicating the presence of nonequilibrium fission processes.