Fission dynamics and entrance-channel study in the Po210 compound nucleus via light-particle multiplicities

Le résumé fourni par la source

Neutron multiplicities, folding angle distribution, mass distribution, and mass-energy distribution are measured for the compound nucleus $^{210}\mathrm{Po}$ populated through the $^{12}\mathrm{C}+^{198}\mathrm{Pt}$ reaction at an excitation energy of 61.6 MeV. The measured neutron multiplicities are compared with the statistical model code joanne2 to extract total fission time for the $^{210}\mathrm{Po}$ compound nucleus. The total fission time $({\ensuremath{\tau}}_{\mathrm{tot}})$ obtained for this system is $(10\ifmmode\pm\else\textpm\fi{}5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ s at 49 MeV and increases to $(23\ifmmode\pm\else\textpm\fi{}5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ at 61.8 MeV excitation energy indicating that dissipation increases with excitation energy. A comparison with ${\ensuremath{\tau}}_{\mathrm{tot}}$ of the $^{18}\mathrm{O}+^{192}\mathrm{Os}$ reaction populating the same compound nucleus indicates the influence of entrance channel mass asymmetry on the fission time. Dynamical model calculations have been performed to understand the fusion dynamics for these reactions and it is observed that the formation time of the compound nucleus increases as we go from the asymmetric to the symmetric entrance channels. Also, these calculations predict that 93% of the total angular momentum lead to the formation of a fully equilibrated compound nucleus for the $^{12}\mathrm{C}+^{198}\mathrm{Pt}$ reaction whereas this percentage decreases to 84%, for the $^{18}\mathrm{O}+^{192}\mathrm{Os}$ reaction indicating a higher percentage of noncompound nuclear processes in the latter case.

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