Mass distribution in11Binduced fission of232Th

Abstract

Formation cross sections of several fission products have been determined using recoil catcher technique followed by \ensuremath{\gamma}-ray spectrometry in ${}^{11}\mathrm{B}$ induced fission of ${}^{232}\mathrm{Th}$ at ${E}_{\mathrm{lab}}=72,$ 60, and 55 MeV. The data show significant admixture of fission from compound nucleus formed by complete fusion as well as targetlike nuclei formed by transfer reaction. Mass distributions for both the fissioning systems have been obtained using the systematics of charge distribution in low and medium energy fission. The mass distribution for complete fusion fission is broad, Gaussian whereas it is asymmetric for transfer induced fission. The evaporation residue cross sections of targetlike nuclei formed in ${}^{232}{\mathrm{T}\mathrm{h}(}^{11}{\mathrm{B},\mathrm{}}^{10}{\mathrm{B}\mathrm{e})}^{233}\mathrm{Pa}$ reaction were also measured. The measured evaporation residue cross sections and the decay probabilities of targetlike nucleus ${}^{233}\mathrm{Pa},$ calculated by the PACE2 code have been used to estimate the proton transfer fission cross sections which were found to be negligible compared to the total transfer cross section for all the projectile energies used. The transfer fission cross section is dominated by alpha transfer fission as inferred by measured forward to backward ratios for several fission products as well as ${Q}_{\mathrm{gg}}$ systematics for the probable transfer reactions. The proportion of transfer fission cross section to the total fission cross section was 15, 17, and 22 % at projectile energies of 72, 60, and 55 MeV, respectively.