Shape evolution and collective dynamics of quasifission in the time-dependent Hartree-Fock approach

Abstract

Background: At energies near the Coulomb barrier, capture reactions in heavy-ion collisions result either in fusion or in quasifission. The former produces a compound nucleus in statistical equilibrium, while the second leads to a reseparation of the fragments after partial mass equilibration without formation of a compound nucleus. Extracting the compound nucleus formation probability is crucial to predict superheavy-element formation cross-sections. It requires a good knowledge of the fragment angular distribution which itself depends on quantities such as moments of inertia and excitation energies which have so far been somewhat arbitrary for the quasifission contribution. Methods: We investigate the evolution of the nuclear density in time-dependent Hartree-Fock (TDHF) calculations leading to quasifission. Our main goal is to extract ingredients of the formula used in the analysis of experimental angular distributions. These include the moment-of-inertia and temperature. We study the dependence of these quantities on various initial conditions of the reaction process. Results: The evolution of the moment of inertia is clearly non-trivial and depends strongly on the characteristics of the collision. The temperature rises quickly when the kinetic energy is transformed into internal excitation. Then, it rises slowly during mass transfer. Conclusions: Fully microscopic theories are useful to predict the complex evolution of quantities required in macroscopic models of quasifission.