SINGLE AND MULTINUCLEON TRANSFER IN F-19, O-16, C-12-232 REACTIONS ATNEAR-BARRIER ENERGIES(TH)

Cross sections for single (1p) and multinucleon (2p,He-4, and p(4)He) transfer reactions have been measured in F-19, O-16, C-12+Th-232 syste ms at beam energies around the Coulomb barrier. Angular distributions and energy spectra of the projectilelike particles exhibit characteris tics of direct transfer reactions. The ratio of the transfer to total reaction (transfer+fusion-fission) cross section is observed to be sig nificantly smaller for the C-12 projectile, as compared to that for F- 19 and O-16 projectiles. All the systems show large transfer cross sec tions relative to the total reaction cross section at subbarrier energ ies. The angular distribution data were analyzed in terms of transfer probabilities to derive the slope parameter (alpha) for the stripping of 1p and 2p in the case of O-16 and C-12 projectiles and for 1p, He-4 and correlated (p(4)He) stripping in the case of F-19 projectile, for comparison with the semiclassical calculations. It is observed that t he semiclassical picture is valid for 1p transfer at energies near the Coulomb barrier, whereas for correlated 2p, He-4, and (p(4)He) multin ucleon transfers, the experimental values of cu are anomalously small as compared to the semiclassical calculations even at subbarrier energ ies. At the above-barrier energies, the slope anomaly can be explained after inclusion of the nuclear effects in semiclassical calculations.