Mass distribution in B-11 induced fission of Th-232

Formation cross sections of several fission products have been determined u sing recoil catcher technique followed by gamma-ray spectrometry in B-11 in duced fission of Th-232 at E-lab = 72, 60, and 55 MeV. The data show signif icant admixture of fission from compound nucleus formed by complete fusion as well as targetlike nuclei formed by transfer reaction. Mass distribution s for both the fissioning systems have been obtained using the systematics of charge distribution in low and medium energy fission. The mass distribut ion for complete fusion fission is broad, Gaussian whereas it is asymmetric for transfer induced fission. The evaporation residue cross sections of ta rgetlike nuclei formed in Th-232(B-11, Be-10)Pa-233 reaction were also meas ured. The measured evaporation residue cross sections and the decay probabi lities of targetlike nucleus Pa-233, calculated by the PACE2 code have been used to estimate the proton transfer fission cross sections which were fou nd to be negligible compared to the total transfer cross section for all th e projectile energies used. The transfer fission cross section is dominated by alpha transfer fission as inferred by measured forward to backward rati os fur several fission products as well as Q(gg) systematics for the probab le transfer reactions. The proportion of transfer fission cross section to the total fission cross section was 15, 17, and 12 cre at projectile energi es of 72, 60, and 55 MeV, respectively. [S0556-2813(99)04906-7].