Time Scale of Fission at High Angular Momentum

Abstract

Spectra of neutrons emitted in coincidence with evaporation residues and fission fragments have been measured in the (192 MeV) $^{12}\mathrm{C}$+$^{158}\mathrm{Gd}$ and (176 and 239 MeV) $^{20}\mathrm{Ne}$+$^{150}\mathrm{Nd}$ reactions. At the two lower energies, several neutrons are evaporated prior to fission. At the highest bombarding energy essentially all the neutrons are evaporated by the fragments indicating that at high angular momentum, the fission process is rapid compared to the time scale for neutron evaporation.