We attempted to characterize by neutron powder diffraction the monoclinic alpha' phase that is known to form at low temperatures in dilute Pu-Ga alloys. This attempt was unsuccessful, as we did not detect any transformation to the alpha' phase, but instead observed a line-broadening effect in the fcc delta phase. This effect is large enough to be visible in the raw diffraction data and is highly anisotropic in crystal space. The onset temperature of the line broadening (150 K) coincides with previous observations of the delta-alpha' transformation. Bulk alpha' was not observed. We believe that the development of alpha' nuclei creates a spatially inhomogeneous stress distribution in the delta matrix, which in turn exhibits an anisotropic response, governed by its elastic anisotropy. We have analysed this observation of anisotropic microstrains in terms of the fictive microstresses required to produce them by elastic deformation. During the course of this work, we found a pseudo-isotope effect in the room temperature lattice constants of Pu-Ga alloys. The alloys made from nominal Pu-242 isotope show systematically higher lattice constants than the corresponding Pu-239 alloys, and the size of the effect is proportional to the Ga concentration. We believe that this effect is associated with the higher levels of radiation damage from isotopic impurities in the Pu-242 alloys.

Much work has been devoted in recent years to identifying ceramic materials that can withstand high doses of radiation without incurring excessive defect accumulation, or suffering undesirable transformations such as amorphization. In this paper, it is proposed that a large range of A2O3–BO2 oxide compositions, with structures related to the fluorite crystal structure, may exhibit exceptional resistance to radiation-induced amorphization. Results of heavy ion irradiations on selected A2O3–BO2 oxide compounds are presented in support of this prediction.