Primary fragment mass-yield distributions for asymmetric fission path of heavy nuclei

The primary fragment mass-yield distribution for the asymmetric fission path in heavy nuclei, ²³³Pa, ²³⁹Np, ²⁴⁵Am and ²⁴⁹Bk at the excitation energy of ∼20 MeV are experimentally constructed based on the intensities of total kinetic energies for individual mass splits. The results revealed an interesting phenomenon: in all the studied fissioning systems, the inner wings of the mass-yield distributions in the asymmetric fission path appear along the same mass-mall of A=130 fragment mass. The asymmetric mass-yield distribution indicates the strong effect of structural shells in fragments on the final mass division process of the asymmetric fission path.