Transient and quasistationary dissipative effects in the fission flux across the barrier in 1A GeV238U on deuterium reactions

Isotopic cross sections of all projectile residues with Z above 23 produced in collisions induced by U-238 at 1A GeV on deuterium have been measured. The isotopic distributions reflect the role of evaporation and fission in the formation process of these nuclei. The comparison of the measured cross sections with Monte Carlo deexcitation codes including an analytical description of the dynamics of fission shows the sensitivity of the data to nuclear dissipation. Moreover, the large excitation-energy range covered in this experiment together with the high accuracy of the measured cross sections allowed to clearly separate and quantify the role of transient and quasistationary dissipative effects in the fission-decay width.