Characterization of the Chemical Composition of Uranium Microparticles with Irregular Shapes Using Standardless Electron Probe Microanalysis and Micro-Raman Spectrometry.

We describe an approach enabling the identification of the elemental composition of uranium microparticles with undefined geometry using standardless quantitative electron probe microanalysis (EPMA) and micro-Raman spectrometry (MRS). The standardless procedure is based on a ZAF peak-to-background quantitative method in combination with Monte Carlo simulations. The experimental X-ray spectra were measured with an energy-dispersive spectrometer attached to a scanning electron microscope. To account for the X-ray intensity loss due to the transmission of electrons in microparticles with irregular shapes, a method was developed enabling the determination of an apparent thickness of the particle by means of the mean distance that electrons travel inside the particle before being transmitted. Size effects were further taken into account by using peak-to-background ratios and performing simulations on a particle with a thickness equal to the apparent thickness. To assess the validity of the standardless procedure in EPMA, weight fractions were determined for NIST homogeneous spherical microparticles of K411 glass and compared to certified ones. The correction of size effects was achieved and lead to accurate quantitative results with absolute relative deviations less than 9%. The model used for the determination of the apparent thickness was validated on the set of spherical K411 particles and enabled us to conduct quantifications on irregularly shaped uranium microparticles. The chemical composition of uranium particles was further investigated using MRS which enabled us to verify the reliability of the results obtained by the standardless approach.