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Low-temperature instability in [sup 242]Pu[sub 0.98]Ga[sub 0.02].

Description: We have made an unsuccessful attempt to make a detailed characterization by neutron powder diffraction of the {delta}-{alpha}' transformation that is known to occur at low temperatures in dilute Pu-Ga alloys. The {alpha}'-structure is a variant of the monoclinic a {alpha}'-phase, except that the lattice constants are a bit different, with some (or all) of the Pu sites partially occupied by Ga. This transformation is easily detected by dilatometric methods because of the 19% volume difference between the {delta} and {alpha}'-phases. In our study, we used 242Pu in a Pu0.98Ga0.02 alloy to minimize neutron absorption and cooled the sample very slowly to maximize the degree of transformation. We did not detect any transformation to the {alpha}'-phase, but instead observed a slight line broadening effect that was visible in the raw data. The onset temperature of the line broadening (150K) coincides with observations of the {delta}-{alpha}' transformation. We have developed two alternative explanations for the line broadening effect: (1) the occurrence at low temperatures of a cubic-tetragonal transformation in Ga-stabilized alloy or (2) the occurrence at low-temperature of a spontaneous anisotropic microstrain that is supported by the highly anisotropic elastic constants of {delta}-Pu.
Date: January 1, 2001
Creator: Lawson, A. C. (Andrew C.); Martinez, B. S. (Barbara S.); Roberts, J. A. (Joyce A.) & von Dreele, R. B. (Robert B.)
Partner: UNT Libraries Government Documents Department