Local atomic structure of alpha-Pu - art. no. 174111

The local atomic structure of alpha -Pu was investigated using x-ray absorp tion tine structure (XAFS) spectroscopy. XAFS spectra were obtained for a z one-refined alpha -Pu and the results were compared to 32-year-old and Ce-d oped (0.34 at. %) samples. X-ray diffraction (XRD) patterns were also measu red for the zone-refined and 32-year-old materials. The extent of the Bragg peaks showed that amorphization of the 32-year-old sample had nor occurred despite the prolonged exposure to self-radiation. Analogous to metastable delta -Pu alloys, the local atomic structure around Pu for the zone-refined material shows the possible presence of noncrystallographic Pu-Pu distance s. Conversely, the Ce and the 32-year-old sample show no evidence for such noncrystallographic distances. Disorder in the Pu local environment was fou nd to be impurity dependent. The Ce-doped sample presented a larger Pu-Pu n earest neighbor disorder than the aged sample, although the total amount of Am. U. and He impurities was actually higher in the aged sample. The local environment around U and Ce impurities is consistent with these elements b eing in substitutional lattice sites. In addition. U and Ce do not introduc e significant lattice distortion to their nearest neighbors. This is consis tent with disorder being more related to the perturbation of the coupling b etween the electronic and crystal structure, or the Peierls-Jahn-Teller dis tortion that generates the monoclinic alpha -Pu structure, and less to stra in fields produced in the vicinity of the impurities.