Evolution of mass and charge asymmetry in damped heavy-ion reactions

Projectile-like fragments have been studied with high A and Z resolution for the damped reactions /sup 238/U+/sup 40/Ca, /sup 48/Ca, /sup 58/Ni, and /sup 64/Ni at 8.5 MeV/nucleon. These dinuclear systems exhibit widely different driving forces. Qualitative agreement between experiment and dynamical nucleon-exchange transport theory is obtained for the first and second moments of the fragment atomic (Z) and neutron (N) number distributions. However, systematic differences exist between the experimental and theoretical average values of Z and N suggesting the need for more realistic driving forces.