On the influence of shell structure in dissipative collisions

A kinematically complete study of the symmetric systems 144Sm+144Sm and 154Sn+154Sm has been performed at energies 30% in excess of the interaction barrier. They have been chosen because of their different internal structure: 144Sm has a closed N = 82 neutron shell and a spherical ground-state configuration; 154Sm with ten neutrons outside this shell is strongly deformed. The observed gross features of both reactions like energy, angular and total mass or element distributions are very similar; the ratio of the mass variances as function of the total kinetic energy loss indicates the number of exchanged nucleons to be comparable in all stages of the reactions. At small energy losses, however, the element distributions of the 144Sm + 144Sm reaction are considerably broader, pointing at an enhanced proton transfer at the cost of the number of exchanged neutrons in this system. This observation is attributed to the influence of the closed shell which seems to block the transfer of neutrons at low excitation energies. These results can be explained quantitatively by the different gradients of the shell-corrected potential energy surfaces of the two systems.