X-ray fluorescence tomography of individual waste fly ash particles

Abstract
Fluorescence tomography is a non-destructive, non-invasive technique that provides information about the internai spatial distribution of each element that emits a detectable fluorescence signal from the measured slice of the sample. The reconstruction proMem for fluorescence tomography is much more difficult than it is for transmission tomography, due to the absorption of thé photons within the excitation and détection paths. The present work présents a reconstruction technique that is based on the SART (Simultaneous Algebraic Reconstruction Technique) algorithm, which has been modified in order to take into account absorption corrections. This technique has been applied to the analysis of individual waste fly ash particles of about 80-150 micron diameters, which have been scanned using an X-ray beam of V*H=2*5 pjn spot-size and placing an energy dispersive Si (Li) X-ray detector at 90 degrees to the incoming excitation beam. From previous scanning i-SRXRP measurements it is clear that the elemental distribution within individual fly ash particles is highly inhomogeneous but no information could be obtained on the location of the différent investigated elements (within/on the surface of the particle). On the other hand thé location of toxic elements within individual fly ash particles affects the possible fate of thèse elements during e.g. fly-ash recycling. Thus the aim of this study was to investigate the 2D interna) elemental distribution of the particles, with spécial attention to that of the toxic metals, such as Zn, Cd, Pb.