Charged particle multiplicities in heavy-ion-induced fission

Abstract

Pre- and post-scission protons and \ensuremath{\alpha} particles are measured in the $^{16}\mathrm{O}$${+}^{197}$Au, $^{19}\mathrm{F}$${+}^{181}$Ta, $^{197}\mathrm{Au}$ and $^{208}\mathrm{Pb}$, and $^{28}\mathrm{Si}$${+}^{197}$Au and $^{208}\mathrm{Pb}$ reactions in the compound nucleus excitation energy range of 43 to 117 MeV. The angular correlation measurements between \ensuremath{\alpha} particles and fission fragments suggest that the pre-scission \ensuremath{\alpha} particles seem to be mainly emitted from spherical compound nuclei or nuclei in an early stage of the fission process before saddle. The pre-scission multiplicities of protons and \ensuremath{\alpha} particles are compared to the statistical model calculations and are reproduced by assuming the ratio ${\mathit{a}}_{\mathit{f}}$/${\mathit{a}}_{\mathit{n}}$ of the saddle point deformation to the ground-state deformation within the limit of 1.00 to 1.02. The post-scission protons and \ensuremath{\alpha} particles are consistent with the evaporations from the fission fragments whose excitation energies are considerably reduced by the pre-scission neutron emissions.