X-ray fluorescence tomography of individual waste fly ash particles

Fluorescence tomography is a non-destructive, non-invasive technique that provides information about the internal spatial distribution of each element that emits a detectable fluorescence signal from the measured slice of the sample. The reconstruction problem for fluorescence tomography is much more difficult than it is for transmission tomography, due to the absorption of the photons within the excitation and detection paths. The present work presents 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 8O 150 micron diameters, which have been scanned using an X-ray beam of V*H=2*5 μm 2 spot-size and placing an energy dispersive Si(Li) X-ray detector at 90 degrees to the incoming excitation beam. From previous scanning μ-SRXRF 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 different investigated elements (within/on the surface of the particle). On the other hand the location of toxic elements within individual fly ash particles affects the possible fate of these elements during e.g. fly-ash recycling. Thus the aim of this study was to investigate the 2D internal elemental distribution of the particles, with special attention to that of the toxic metals, such as Zn, Cd, Pb.