Monte Carlo + molecular dynamics modeling of radiation damages in Pu

The paper describes calculations on the evolution of damage cascades in self-irradiated unalloyed and gallium-alloyed δδ-Pu. The fast stage of the evolution was simulated by the Monte Carlo (MC) method. When the energies of cascade particles became close to the displacement energy, the cascade configuration was transferred to a molecular dynamics (MD) code which tracked the further evolution of the system to ∼∼ 2 ns. The simulations showed that a cascade of damages from the U recoil nucleus caused a large energy release into a lattice subsystem within a local region about 10 nm in size where the material melted and then recrystallized. Preliminary estimates showed that the energy transferred to the lattice was enough to cause melting in a region whose characteristic size was ∼∼ 15 nm (∼∼ 200,000 atoms). MD simulations showed heat conductivity to reduce the characteristic size of the melting region to ∼∼ 8 nm (∼∼ 12,000 atoms) in a sample whose initial temperature was 300 K. The time of recrystallization was estimated to be ∼∼ 1 ns. It was shown that most point defects created during the fast stage of the cascade were recovered in melting and recrystallizing. A number of calculations were also done for polycrystalline samples.