Two-proton transfer reactions induced by 56-MeVO16heavy-ion beam onNi64andGe76target isotopes

An optical model and distorted-wave Born-approximation analysis of elastic scattering one- and two-nucleon transfer angular distributions was employed phenomenologically to determine an optical model potential which reproduced simultaneously the elastic scattering and nucleon transfer data. This potential was found to have an imaginary part of smaller radius than the real one. The relatively weak absorption in the tail region of the optical potential was necessary for the oscillatory behavior at forward angles observed on the direct two-proton transfer angular distributions. The periodicity of these oscillations was $\frac{180°}{l_c}$, $l_c$ being the grazing partial wave corresponding to the half-absorption radius of the strong absorption model. For the ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$)${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$ reaction, the anomalous behavior of the angular distribution of the first $2^{+}$ excited level of ${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$ favored a two-step mechanism involving core excitation of the target and/or residual nucleus.