EVALUATING THE GRAPHITE THERMAL NEUTRON SCATTERING LAW USING MOLECULAR DYNAMIC CORRELATION FUNCTIONS

摘要

The thermal neutron scattering law is an important factor governing the slowing-down of neutrons below about 1 eV. Typically, calculations of the scattering law through atomistic simulation impose a ponderous computational burden when the symmetry of the scattering system is broken as a result of irradiation defects or imperfections. In this study, the theory of thermal scattering is presented in the framework of classical time correlation functions that are easily accessible from the most basic output of molecular dynamic (MD) simulations. These techniques work just as efficiently with imperfections as without, and are also suitable for modeling the defect accumulation processes responsible for lattice damage in a reactor environment. In this work, classical MD scattering law calculations are performed for graphite. An MD code especially designed for the study of graphite was utilized. As part of the validation of this approach, the Green-Kubo method is employed to compute the basal plane thermal conductivity of graphite between 300 K and 1800 K. Good agreement is observed with experimental conductivity data throughout the investigated range of temperatures.