Influence of Shell Structure on Neutron and Proton Exchange in the Reactions ofSm144onSm144andSm154onSm154

The reactions of ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ on ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ on ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ have been studied at energies 30% in excess of the barrier. Whereas the number of exchanges nucleons is similar in both reactions, the number of exchanged protons is considerably larger at small energy losses in the ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ system. On the basis of the shell-corrected liquid-drop potential energy surface these observations are attributed to the closed $N=82\mathrm{}$ neutron shell which, for ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$, hinders the neutron exchange and leads to a preferential transfer of protons.