Probing of fusion fission dynamics in mass region of A 200

Abstract

The fusion fission dynamics of the compound nucleus 201Bi have been investigated using two different entrance channels, 16O+185Re and 31P+170Er, over an excitation energy range of 62 85 MeV. Average neutron multiplicities were measured using the National Array of Neutron Detectors (NAND) at IUAC, New Delhi, with a dedicated setup enabling the extraction of both pre-scission and post-scission neutron components from the neutron energy spectra. A clear entrance-channel dependence is observed: as mass symmetry increases, the formation time of the compound nucleus becomes longer, leading to the evaporation of a larger number of neutrons during the formation stage for the more symmetric 31P+170Er reaction. These findings demonstrate that entrance-channel mass asymmetry and target deformation significantly influence the timescales and dissipation mechanisms governing the fusion fission process in low-fissility nuclei such as Bi. newline