Microscopic models of nuclear reactions near the Coulomb barrier

Abstract

A complete understanding of dynamic behaviour of a strongly interacting quantum many-body system like the atomic nucleus remains elusive. Nuclear reactions at energies near the Coulomb barrier are uniquely sensitive to quantum effects. In particular, collective tunnelling and nuclear shell effects are important to the dynamics of these reactions.

Mean-field techniques allow for effective microscopic models of the nucleus but there are still remaining challenges. How should a mean-field based approach be generalised to describe collective tunnelling of strongly interacting systems? Can mean-field simulations replicate the shell effects seen in formation of fission fragments, and would they depend on the history of the system? One way to address this question is to compare mean-field simulations of quasifission (damped heavy-ion collisions with significant mass equilibration) and fission of a compound nucleus.

An imaginary time extension to mean-field theory was tested, which reproduced collective tunnelling behaviours and their probabilities. Fission was studied through the production of potential energy surfaces via a constrained Hartree-Fock calculation. Quasifission of heavy and superheavy systems was studied via time-dependent Hartree-Fock calculations.

The imaginary time theory was shown to have potential but encounters some difficult numerical challenges. The potential energy surfaces revealed features identified with shell effects driving fission in both actinide thorium and superheavy oganesson nuclides. Mapping the quasifission trajectories onto the calculated potential energy surfaces provided useful information about how the shell effects in fission relate to quasifission.

An approach to analyse quasifission dynamics using the topology of the underlying compound nuclear potential energy surface was proposed. The strength of mean-field models for testing and understanding nuclear near-barrier dynamics was confirmed. The correspondence between microscopic and collective degrees of freedom in different reactions is of importance, and resulting models can be tested with experiment. Show more