First-chance fission probability and presaddle nuclear dissipation

Dissipation retards fission, resulting in a drop in the first-chance fission probability of a fissioning nucleus with respect to its statistical model value. We use the Langevin model to compute the evolution of the drop(due to friction), P_(f0)^(drop), for the fissioning systems^(220)Th and ^(240)Cf with the presaddle friction strength(b). The firstchance fission probability is shown to depend sensitively on b, and the sensitivity is apparently greater than that of the total fission probability. We further find that although the total fission probability of heavy ^(240)Cf is insensitive to b, its first-chance fission probability is quite sensitive to b.These results suggest that, to strongly limit the presaddle friction strength, an optimal experimental avenue is to measure the first-chance fission probability of heavy fissioning nuclei.

Dissipation retards fission, resulting in a drop in the first-chance fission probability of a fissioning nucleus with respect to its statistical model value. We use the Langevin model to compute the evolution of the drop （due to friction）, pf0^drop , for the fissioning systems ^220Th and ^240Cf with the presaddle friction strength （β）. The firstchance fission probability is shown to depend sensitively on fi, and the sensitivity is apparently greater than that of the total fission probability. We further find that although the total fission probability of heavy ^240Cf is insensitive to fi, its first-chance fission probability is quite sensitive to ft. These results suggest that, to strongly limit the presaddle friction strength, an optimal experimental avenue is to measure the first-chance fission probability of heavy fissioning nuclei.