Transient times for nuclear fission

Viewing fission as a diffusion process over the fission barrier, Kramers showed many years ago that the stationary part of the diffusion current as calculated from a Fokker-Planck equation gives an expression for the fission width which is essentially identical to the Bohr-Wheeler formula. Stationarity is reached after a transient time which is controlled by the nuclear friction constant γ. Transients may therefore yield information on the size of γ. Several experiments show that the number of neutrons emitted prior to fission in light ion induced reactions at excitation energies of several ten MeV is larger than predicted by the statistical model. They have analyzed some of this material, and have obtained an upper bound on γ. Possible extensions of this work, and implications for spontaneous fission, will be discussed