Systematics of pre- and near-scissionα-particle multiplicities in heavy-ion-induced fusion-fission reactions

Abstract

The $\ensuremath{\alpha}$-particle energy spectra have been measured in coincidence with fission fragments over a wide range of relative angles with respect to fragment emission direction in the ${}^{11}$B (62 MeV) $+$ ${}^{232}$Th reaction. The $\ensuremath{\alpha}$-particle multiplicity spectra have been fitted with moving source model to extract the prescission (${\ensuremath{\alpha}}_{\mathrm{pre}}$) and near-scission (${\ensuremath{\alpha}}_{\mathrm{nse}}$) components. The present results, along with available data from the literature over a wide range of ${Z}^{2}/A$ and the excitation energy of a compound system, have been analyzed to develop certain global features of the pre- and near-scission emission characteristics. It is seen that ${\ensuremath{\alpha}}_{\mathrm{pre}}$ values when normalized to ${E}_{\mathit{CN}}^{2.3}$ (${E}_{\mathit{CN}}$ is the compound nucleus excitation energy) show a systematic linearly increasing trend with the $\ensuremath{\alpha}$-particle emission $Q$ value (${Q}_{\ensuremath{\alpha}}$). The fraction of near-scission multiplicity is observed to be nearly the same at around 10% of the total prescission multiplicity for all the systems.