Charged particle multiplicities in heavy-ion-induced fission

Pre- and post-scission protons and α 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 α particles and fission fragments suggest that the pre-scission α 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 α 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 α particles are consistent with the evaporations from the fission fragments whose excitation energies are considerably reduced by the pre-scission neutron emissions.