Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape

A theory of the competition between fusion and quasifission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasifission arise from a diffusion process in an ensemble of nuclear shapes, each of which evolves toward the thermal equilibrium. The fusing system moves on a dynamical (time-dependent) collective potential energy surface that is initially diabatic and gradually becomes adiabatic. Calculations for several reactions leading to No256 are performed within a simplified two-dimensional model. Among other important conclusions, the results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems and (ii) very asymmetric reactions induced by closed-shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.