Verifying the presence of low levels of neptunium in a uranium matrix with electron energy-loss spectroscopy

This paper examines the problems associated with analysis of low levels of neptunium in a uranium matrix with electron energy-loss spectroscopy (EELS) on the transmission electron microscope (TEM). The detection of neptunium in a matrix of uranium can be impeded by the occurrence of a plural scattering event from uranium (U-M 5 + U-O 4,5) that results in severe overlap on the Np-M 5 edge at 3665 eV. Low levels of Np (1600–6300 ppm) can be detected in a uranium solid, uranophane [Ca(UO 2) 2(SiO 3OH) 2(H 2O) 5], by confirming that the energy gap between the Np-M 5 and Np-M 4 edges is at 184 eV and showing that the M 4/M 5 ratio for the neptunium is smaller than that for uranium. The Richardson–Lucy deconvolution method was applied to energy-loss spectral images and was shown to increase the signal to noise ratio.