Research on long-time self-irradiation of alloy δ-Pu242–Ga

Self-irradiation of Pu–Ga alloy was studied by neutron diffraction, which provided information about the crystalline structure and yielded mean-square atom displacements 〈u2〉 from the Debye–Waller factor. The measurements were performed at room temperature using the sample based on the isotope Pu242 with low neutron absorption cross-section to which the short-living isotope Pu238 (1.4%) was added to accelerate self-irradiation. This composition of the sample sped up the aging processes by the factor of four and allowed us to obtain the maximum equivalent time of 23.5 years. Fcc structure remains the same throughout this interval. The changes in 〈u2〉 due to static displacements occur in two stages, viz. a relatively rapid growth (roughly by 50%) over the first 5–6 equivalent years and slow decline during 6–23 equivalent years making a close approach to the initial values. The latter stage has not been described in the literature. It can be explained by the confluence of point defects into helium bubbles and dislocation loops accumulated over time.