Analysis of dissipative effects in nuclear fission observed in the fragmentation of 238U projectiles

The abrasion-ablation model widely used previously to describe peripheral nuclear reactions at relativistic energies has been generalized to be applicable to heavy reaction partners for which it is important to account for nuclear fission. It is shown that the changes of the fission widths and the transient times of the competing decay modes caused by the nuclear viscosity must be included to consistently describe the available experimental data. The model predictions are in good agreement with measured total fission cross sections for high-energy 238U projectiles impinging on different targets. Furthermore, recently measured production cross sections of neutron-deficient U and Pa isotopes in the fragmentation of 238U projectiles at 950A MeV are well described by the model, if a nuclear viscosity parameter of β=1x1021 s-1 is chosen. The model predicts rather high production cross sections for a wide range of fissile exotic nuclei which may be produced by the fragmentation of 238U. (orig.)