Empirical identification of uranium oxides and fluorides using electron energy-loss spectroscopy in the transmission electron microscope

A set of uranium compound particles relevant to contaminated soils and othe r environmental concerns surrounding uranium bioavailability were studied b y electron energy-loss spectroscopy (EELS). Core-loss EELS results suggest that uranium 4(+) compounds have an energy loss resolvable from 6(+) compou nds. Shoulders on the uranium O-4,O-5 edge further distinguish UO2 from UF4 . Low-loss characteristics distinguish carbon-free uranium oxide specimens on holey substrates. In the presence of carbon, correction techniques must be applied. Uranium oxides, fluorides, and minerals show a tendency toward reduction of uranium toward 4(+) under the beam. The electron dose required to achieve the transformation from 6(+) to 4(+) is more severe than that u sually required to obtain satisfactory spectra, but the possibility for red uction should be considered. The conditions for low-loss analysis need not be as vigorous as those for core losses, and can be done without altering t he valence of most oxides.