Comparison of nuclear and X-ray techniques for actinide analysis of environmental hot particles

Abstract

Actinide-containing radioactive hot particles have been dispersed into the environment during atmospheric nuclear tests, accidents of the nuclear fuel cycle and authorized discharges from nuclear reprocessing plants. Several other activities like illicit trafficking of radioactive material or the use of depleted uranium in shielding, weapons can also be considered as possible sources of contamination by actinides. The paper compares detection limits for actinide analysis by nuclear spectroscopy as well as various X-ray micro-fluorescence and absorption techniques using laboratory and synchrotron sources. The detection limits for X-ray techniques were calculated using Monte Carlo simulations. Detection limits obtained for X-ray microanalysis using synchrotron sources were close to that of nuclear analysis. For long half-life nuclides (more than 10⁵ years), X-ray spectrometry was more sensitive, while being non-destructive and offering additional information on oxidation states using X-ray absorption. For U, α spectrometry resulted only in 10⁻⁷ g (²³⁸U) contrasting 10⁻¹³ g obtained for monochromatic beam µ-XRF (micro X-ray fluorescence) at HASYLAB Beamline L. Using the combination of autoradiography and µ-XRF, identification and quantitative analysis of individual radioactive particles of 20 µm diameter were possible. Despite the strong spectral overlap with the Rb-Kα characteristic line, in fluorescence mode µ-XANES (micro X-ray absorption near-edge structure) it was possible to determine the oxidation state of 15 µg g⁻¹ U in a single hot particle.