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

The multiplicities of alpha particles and neutrons have been measured simultaneously for the reaction O-16 + Pt-196 forming Rn-212 compound nucleus at excitation energies of 56 MeV, 61 MeV, and 68 MeV. Neutrons and alpha particles were detected at various angles in coincidence with the fission fragments. To extract the contribution of pre- and postmultiplicities using the total alpha-particle and neutron spectra, moving source formalism was implemented. In the case of alpha 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 alpha particles by varying the transient (tau(tr)) and saddle to scission (tau(SSC)) times. It is found that the fission time scales of the order of 50-70 x 10(-21) sec are required to reproduce the neutron and alpha-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.