Quantal nucleon diffusion: Central collisions of symmetric nuclei

The quantal diffusion mechanism of nucleon exchange is studied in the central collisions of several symmetric heavy ions in the framework of the stochastic mean-field (SMF) approach. Since, at bombarding energies below the fusion barrier, dinuclear structure is maintained, it is possible to describe nucleon exchange as a diffusion process familiar from deep-inelastic collisions. Quantal diffusion coefficients, including memory effects, for proton and neutron exchanges are extracted microscopically employing the SMF approach. The quantal calculations of neutron and proton variances are compared with the semiclassical results.