Puzzling features of heavy-ion fission at sub-barrier energies

Abstract

The heavy-ion induced fission fragment angular distributions measured for systems with Th, U and Np as targets have revealed "anomalous" values of anisotropies at energies E≤V_B (fusion barrier) and this feature is observed to be independent of the entrance channel mass-asymmetry. While this puzzling feature is exhibited by the deformed targets like Th, U and Np, most of the fission data measured for the spherical targets like Pb and Bi can be satisfactorily explained using the standard saddle point statistical model with moderate correction for pre-fission neutron emission. Plausible reasons for this anomalous behaviour are explored.