Single and multinucleon transfer in19F,16O,12C+232Th reactions at near barrier energies

Abstract

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