Collision cascades in pure δ-plutonium

Abstract

Molecular dynamics simulations of the formation and annealing of large collision cascades in delta-phase plutonium are presented. The defect evolution is followed with time up to 2 ns. Simulations are performed with the MEAM potential at three different temperatures; at 600 K where the pure delta phase is thermodynamically stable; at 300 K where the delta phase can only be maintained in a metastable state with minor additions of gallium or aluminum; and at 180 K where plutonium should transform to the alpha phase. It is found in all three cases that the atomic structure within the cascade evolves through a glass-like state. At 600 K, this structure recovers very slowly; at 300 K it persist up to 2 ns with no discernable trend to recover eventually; and at 180 K the amorphous structure initiated by the collision cascade spreads through the entire crystal and converts it to a glass-like structure.