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

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