Affirmation of transfer-breakup as a source for α -particle emission in C12,13+Th232 fission reactions

Abstract

An enhancement in near-scission $\ensuremath{\alpha}$-particle multiplicity was observed in the $^{12}\mathrm{C}+^{232}\mathrm{Th}$ fission reaction at a beam energy of 69 MeV in a recent experiment [Y. K. Gupta $et\phantom{\rule{4pt}{0ex}}al.$, Phys. Rev. C 86, 014615 (2012)]. The excess $\ensuremath{\alpha}$-particle emission was attributed to $\ensuremath{\alpha}$-transfer induced fission, where $\ensuremath{\alpha}$-particle transfer followed by breakup of $^{8}\mathrm{Be}$ into two $\ensuremath{\alpha}$ particles in coincidence with fission fragments (FFs) was observed. In order to further verify this transfer-breakup source, $\ensuremath{\alpha}$-particle energy spectra have been measured in coincidence with FFs in $^{12,13}\mathrm{C}+^{232}\mathrm{Th}$ reactions at various relative angles with respect to the beam and FF directions at a beam energy of 74.5 MeV. The $\ensuremath{\alpha}$-particle multiplicity spectra were fitted using a moving source disentangling analysis. The features of multiplicity spectra clearly demonstrate the presence of transfer-breakup events in $^{12}\mathrm{C}+^{232}\mathrm{Th}$ fission. The contribution of $\ensuremath{\alpha}$-particle multiplicity from transfer-breakup events in the $^{13}\mathrm{C}+^{232}\mathrm{Th}$ reaction is seen to be negligibly smaller than that of the $^{12}\mathrm{C}+^{232}\mathrm{Th}$ reaction. After taking into account the transfer-breakup source, the pre- and near-scission $\ensuremath{\alpha}$-particle multiplicities follow the recently developed heavy-ion systematics for both reactions. These results conclusively affirm that transfer-breakup is a potential source of $\ensuremath{\alpha}$-particle emission in fission reactions, induced by $\ensuremath{\alpha}$-cluster projectiles such as $^{12}\mathrm{C}$.