Comparison of one- and two-proton transfer in 32S+92,98,100Mo, 93Nb at energies near the Coulomb barrier.

Abstract

One- and two-proton stripping cross sections were measured for $^{32}\mathrm{S}$${+}^{92,98,100}$Mo and $^{93}\mathrm{Nb}$ systems at laboratory energies of 125, 116, and 109 MeV. The angular distributions were compared with distorted wave Born approximation calculations where reasonable agreements were shown for one-proton stripping. The two-proton transfer probability shows an anomalous dependence on distance of closest approach at energies above the Coulomb barrier for all targets. This slope anomaly disappears at energies below the barrier. A simple model suggests that the one-proton transfer mechanism at these energies is dominated by semiclassical dynamics, while for two-proton transfer at energies above the barrier a diffraction process is dominant due to localization in angular momentum space.