Self-diffusion in plutonium metal

Abstract

We have determined self-diffusion coefficients for the epsilon, delta prime, delta, gamma, and beta phases of polycrystalline plutonium by the “thin film” tracer tech-nique, and fine sectioning. Our experiments encompassed a sample temperature range from 393 to 886 K. The corresponding diffusion times ranged from about 4 h to one year. Although our results for the epsilon phase corroborate those of others, our lattice diffu-sivity values for the delta and gamma phases differ significantly from previously reported values. Our D₀ value for delta plutonium is two-orders-of-magnitude higher than pre-viously reported and our activation energy is about 30 pct higher. However, in contrast to other studies, our measurements for the delta plutonium phase covered the entire temperature-stability range. Diffusivity values for the delta-prime phase have not previ-ously been reported. Our diffusivity measurements are reasonable, although ourD ₀ value and the activation energy derived by least squares are questionably high. We have ob-tained new values for lattice diffusivities for the gamma and beta phases. Values for the latter have not been previously reported. We interpret relatively high diffusivities re-ported earlier for the gamma phase as resulting from short-circuit path effects. The usual concentrationvs penetration curves reported here for gamma and beta phases are analyzed in terms of dislocation and other short-circuit paths. The finer sectioning technique used in this study allowed us to separate the true lattice diffusivities from the short-circuit effects found in our gamma- and beta-phase measurements.