A microscopic study of nuclear fission using the time-dependent Hartree-Fock method

• Main Author: Goddard, Philip M
• Format: Dissertation
• Language: English
• Published: University of Surrey 2014

This thesis is concerned with the application of the time-dependent Hartree-Fock method, adopting the Skyrme effective nuclear interaction, to investigate induced nuclear fission processes. Three-dimensional, symmetry-unrestricted constrained Hartree-Fock calculations of ²⁴⁰Pu are presented to obtain the static potential energy surface corresponding to an increasing quadrupole deformation. The time-dependent Hartree-Fock method is applied to evolve in time these deformed states. Different types of fission process are considered. Firstly, the evolution of static configurations which are deformed sufficiently such that they fission upon time evolution, without any external excitation, ('deformation-induced' fission) is investigated. The fragments smoothly form during a gradual evolution of the static state (taking up to ≈ 1500 fm/c for scission to occur), and the resulting fission products agree well with experimental neutron-induced fission data. The kinetic energy released in the process is also shown to compare well to experimental results. Secondly, the effect of providing an external excitation field to static configurations which would not otherwise fission ('boost-induced' fission) is investigated. Upon application of an instantaneous excitation, the evolution of the densities displays a violent oscillatory behaviour as the state evolves to fission, in contrast what was seen for the case of deformation-induced fission. The resulting fission products lie at the edges of typical mass distributions obtained from experiment. The evolution of the densities following the application of a gradual excitation field demonstrates behaviour similar to deformation-induced fission, suggesting that the timescale for the energy deposition has consequences regarding the fission dynamics. The comparison to experimental results following the application of a gradual excitations field is improved compared to an instantaneous excitation. Overall, the results provide a significant exploratory investigation of fission treated as a dynamic process, and suggest that the time-dependent Hartree-Fock method has potential to be applied further to describe the dynamics of nuclear fission.