Investigation of fusionldistributions at near and sub-barrier energies through fission fragmentγray multiplicity measurements

Abstract

Measurements of fission fragment gamma ray multiplicity distributions were carried out at near and sub-barrier energies in ${}^{12}$C, ${}^{16}$O + ${}^{232}$Th reactions. The results were analyzed to determine the average values of the total fragment spin, which were used to deduce the average spin of the compound nucleus $〈l{〉}_{\mathrm{CN}}.$ It is observed that $〈l{〉}_{\mathrm{CN}}$ decreases smoothly with decreasing bombarding energy and saturates as the energy falls through the barrier, thereby resembling features analogous to those predicted by various fusion models. The present results do not indicate any anomalous feature in the $〈l{〉}_{\mathrm{CN}\mathrm{}}$ at the sub-barrier energies, which imply that the recently observed anomalous fragment anisotropies in these systems are not due to anomalous broadening of fusion $l$ distributions but may result from the narrowing of $K$ distribution in the fission process.