dc.description.abstract
X-ray fluorescence (XRF) imaging is a widely used tool for the determination of the spatial distribution of elements in a sample. We developed and implemented a method for full-field XRF imaging based on coded apertures (CA) at the BAMline at BESSY II (HZB). This technique has its origins in astrophysics [1, 2], and is also used in nuclear medicine [3] or radiation detection, e.g., for nuclear decommissioning [4]. The principle of CA based XRF imaging has already been described [5, 6], and a coded aperture microscope for X-ray fluorescence full-field imaging has been designed and constructed recently at NSLS [7].
Detector
Mask Fluorescent X-rays
Incoming X-rays
Sample
Figure 1: The principle of X-ray fluorescence imaging with coded apertures.
In short, the whole sample is irradiated by X-rays, causing fluorescence radiation, which falls through a mask with known hole pattern, called coded aperture, onto an area sensitive detector. As the recorded image consists of overlapping projections of the object, a reconstruction step is performed to retrieve the image information. Figure 1 shows a general scheme of the experiment.
In this work, we present the first experiments on a test sample containing different elements. We performed measurements with a coded mask based on a modified uniformly redundant array [8] with an energy-dispersive 2D detector, the SLcam [9].
Different reconstruction methods were tested [10]. The best results were achieved with an iterative algorithm, and are presented here. We could obtain resolution that are better than predicted for a single pinhole with the same diameter as the pinhomes in the CA.
Furthermore, we performed simulations to test the performance of the reconstruction, and to provide a basis for further investigations of the ideal parameters for near field CA imaging and for refinement of the algorithms.
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[9] Scharf, O., et al., Anal Chem, 83(7), 2011, 2532-8.
[10] Kulow, A., et al., J. Anal. At. Spectrom., 35, 2020, 1423-1434.
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