Relative thresholds for production of iodine isotopes from fusion and transfer-induced fission reactions

The reaction of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ions with energies from 212 to 340 MeV impinging on a thick ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ target has been studied using radiochemical methods. The formation cross sections of iodine isotopes were measured and converted to independent yields from which isotopic distributions were derived. The observed shape of the iodine distributions is attributed to entrance channel mechanisms: quasielastic transfer, deep inelastic transfer, and complete fusion, each followed by fission. The width and shape of the complete fusion component are found to be consistent with the statistical model for fission and a standard evaporation code for the fragment deexcitation. The threshold for production of iodine isotopes by the complete fusion reaction is found to be at least 8 to 12 MeV higher in energy than the barrier for the production of iodine isotopes by the quasielastic transfer reaction. These barriers are compared with theoretical predictions.