FISSION DYNAMICS OF HOT NUCLEI AND NUCLEAR DISSIPATION

The time scale of the fission process at moderate to high excitation e nergies is determined by shape-dependent and, most likely, temperature -dependent nuclear dissipation. Most of our present knowledge about th e time scale of nuclear fission has been deduced from measurements of multiplicities and the energy spectra of neutrons, light charged parti cles, and gamma-rays evaporated or emitted prior to and after scission . Together with complementary data such as fission probabilities, it i s possible to obtain a reasonable description of the time evolution of nuclear fission. The magnitudes of nuclear dissipation, deduced from pre and postscission neutron multiplicities, are compared with the res ults of recent theoretical dynamical models. The status of the experim ental results pointing to a relatively slow fission process and cold s cission. as well as the corresponding theoretical interpretation of th ese findings, are reviewed.