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MD Modelling of Primary Damage Production in Displacement Cascades

Friday, July 27, 2007 - 3:00pm - 3:20pm
EE/CS 3-180
Roman Voskoboynikov (University of Cambridge)
Displacement cascades are the primary source of radiation damage of reactor structural materials exposed to fast-neutron irradiation. They are formed by the recoil of primary knock-on atoms with a kinetic energy of more than ~1 keV. The cascade process is characterized by lengths and times of the order of nm and ps, respectively, and it can be modelled by the method of molecular dynamics.
At a time in the early stage of a cascade, only a small proportion of atoms recoil with high velocity while the rest satisfy the equilibrium velocity distribution for the ambient temperature. Because the convergent integration timestep is determined by the velocity of the fastest atom, conventional techniques that use fixed step-size integration over the entire ensemble are impractical at that stage. To obtain reasonable computational efficiency we decomposed the ensemble into evolving subsets of ‘cold’ and ‘hot’ atoms and conducted integration of the equations of motion using variable time-step. Four different techniques were applied to identify point defects and point defect clusters created in displacement cascades and determine the size of clusters and their morphology.