Role of viscosity in fusion-fission dynamics via simultaneously measured neutron and α -particle multiplicities

Abstract

The multiplicities of α particles and neutrons have been measured simultaneously for the reaction O16+Pt196 forming Rn212 compound nucleus at excitation energies of 56 MeV, 61 MeV, and 68 MeV. Neutrons and α particles were detected at various angles in coincidence with the fission fragments. To extract the contribution of pre- and postmultiplicities using the total α-particle and neutron spectra, moving source formalism was implemented. In the case of α particle, near scission contribution has also been extracted. Study of the fission mechanism using light particle emissions are helpful in understanding the detailed fusion-fission reaction dynamics. The statistical model code joanne2, which includes deformation-dependent particle transmission coefficients, binding energies and level densities, has been used to reproduce the measured multiplicities of neutrons and α particles by varying the transient (τtr) and saddle to scission (τssc) times. It is found that the fission time scales of the order of 50-70×10-21 sec are required to reproduce the neutron and α-particles multiplicities simultaneously. The fission time scales are the measure of the nuclear viscosity, which is responsible for the dynamic hindrance of the fission process. © 2019 American Physical Society.