Evolution of uranium fission-fragment charge yields with neutron number

We use the Brownian shape-motion model, with its recent extensions, which allow modeling of odd-even staggering, to calculate the evolution of fission-fragment charge distributions with neutron number for the compound-system sequence U-234, U-236, U-238, and U-240. We compare to experimental data where available, for neutron-and electromagnetic-induced fission over a compound-nucleus excitation energy range from about 6 to 20MeV. A notable result of the study is that the evolution of the location of the peak charge yield from Z = 54 in U-234 towards Z = 52 in heavier isotopes, seen in the experimental data, is present also in the calculated yields. We further show that to describe yields at higher compound-nucleus excitation energies, then, already at 20MeV, it is necessary to take multi-chance fission into account.