Statistical and dynamical aspects of the description of the cross section for U-238 fission induced by 1- to 55-MeV neutrons

On the basis of statistical theory and on the basis of the Kramers and Gran ge-Weidenmuller diffusion model of fission, the cross section sigma (f)(E-n ) for U-238 fission induced by 1- to 55-MeV, neutrons is calculated under t he assumption that dynamical effects are damped at low excitation energies. It is shown that the structure of the fission cross section from a statist ical calculation differs Substantially from that in a dynamical description . The reduced coefficient of nuclear friction (viscosity) is found to be be ta = 4.1 X 10(21) s(-1). This value and the estimate beta > 5 x 10(21) s(-1 ), which was obtained by analyzing the mean multiplicity of prefission neut rons in heavy-ion-induced fission reactions, suggest supercritical damping and the one-body mechanism of nuclear viscosity. (C) 2001 MAIK "Nauka/Inter periodica".