We are using the techniques of neutron and x-ray powder diffraction to learn more about the driving forces for structural transformations in Pu metal. This research is currently being conducted in three areas: (1) understanding the low melting point of Pu, (2) measuring the intergranular stresses that arise in solid-solid phase transitions of Pu, and (3) determining whether the idiosyncratic crystal structures of Pu are stabilized by Pu atoms in different valence states at different crystallographic sites.

In an earlier paper (Lawson et al., 2000, Phil. Mag. B, 80, 53) we described the measurement and interpretation of Debye-Waller factors in a delta -phase Pu0.98Ga0.02 alloy. We concluded that the measurements could be described using a Debye model with a strongly temperature-dependent Debye-Waller temperature. In those experiments, we observed significant diffuse scattering in the neutron powder diffraction patterns. In this paper we describe a new technique for analysing diffuse scattering based on Rietveld analysis, and apply the technique to data for F-phase Pu0.98Ga0.02 and for Pb. The results from the correlations among lattice vibrations show that the diffuse scattering is Warren-Borie scattering and that the diffuse scattering is in basic agreement with that expected from the Debye model except that the scattering from the nearest-neighbour correlations in Pu0.98Ga0.02 is anomalous at high temperatures. We also discuss the observation of significant anisotropic broadening of the diffraction peaks for Pu0.98Ga0.02 at low temperatures.