2, Lawrence Berkeley National Laboratory, Berkeley, California, United States
The radioactive decay processes at work in plutonium produce a complex set of changes in the material. In addition to ever-changing chemical makeup, defect structures are continuously created by radiation damage, and annealed by multiple processes that are activated at various temperature regimes. Our initial work in this area involved storing a sample of plutonium at liquid helium temperatures to turn off all natural annealing, and probing the local structure of Pu and Ga atoms as the sample was warmed through various stages of an isochronal annealing experiment. This demonstrated the differing damage and annealing behaviors of Pu and Ga in the lattice.
More recent investigations have repeated these measurements on additional samples. In addition, we have investigated the effects on local structure of high temperature annealing using materials of varying ages and Ga concentrations, leading to an improved understanding of the response of Pu and Ga local structure in different states of sample damage.