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(3)OH)(2)(H(2)O)(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.