Near-scission emission of intermediate mass fragments in $^{12}$C+$^{232}$Th at E/A=16 and 22 MeV
Résumé
Intermediate mass fragments (IMFS) (IMF: 3<~ZIMF<~20) observed in coincidence with two correlated fission fragments following incomplete fusion in $^{12}$C+$^{232}$Th at E/A=16 and 22 MeV are investigated. IMFs emitted prior to significant deformation of the fissioning system, as well as IMFs emitted near scission, are distinguished based upon their characteristic kinetic energy and angular distributions. The yield distributions of IMFs emitted near scission in these12C induced reactions are compared with near-scission IMF yields in spontaneous and low-energy ternary fission. Comparisons are made to both experimental fusion-evaporation data and theoretical predictions of a statistical model. The excitation energy dependence of relative IMF yields for both isotropic and near-scission emission is also presented. Our results for near-scission emission suggest that the production of IMFs near scission is inconsistent with a statistical emission mechanism in which emission barriers follow a standard Z dependence. Dynamical model calculations are used to investigate the role of dissipation, angular momentum, N/Z, and kinetic energy on the fragment formation near scission.