Heavy-ion versus 3He/4He fusion-fission reactions: Angular momentum dependence of dissipation in nuclear fission

The stochastic Langevin model is employed to study dissipation properties in fission in the O-16 + Ta-181 -> Tl-197 system by analyzing prescission neutron yields measured in this reaction. It has been found that the Tl-197 nuclei undergo fission that is not in accordance with the standard Bohr-Wheeler statistical theory. A detailed comparison with previously published work in which fission excitation functions measured in He-3,He-4 + Au-197 -> Tl-200,Tl-201 are shown to be in excellent agreement with the fission width formula predicted by the traditional models of nuclear fission suggests that nuclear dissipation strength may have an angular momentum dependence in addition to the known deformation and temperature dependence. Implications for the basic understanding of the observed abnormal rise in prescission particles at high energy and the need for further experimental confirmations are discussed.