Advanced Data Processing for Full-Field PIXE Imaging

The combination of a pnCCD-based detector with a poly-capillary X-ray optics was installed and examined at HZDR [1]. The set-up is intended for PIXE imaging with protons (2-4 MeV) to survey large, polished geological samples with respect to their trace elemental composition. The X-ray optics is used to guide the emitted photons towards the pnCCD-chip divided into nearly 70000 pixels with dimensions of 48 × 48 µm². By applying a dedicated sub-pixel algorithm to recalculate the footprint of the photon’s electron cloud in the chip [2], this limitation can be bypassed and the resolution is then mainly determined by the capillary’s diameter of 20 µm.
Nevertheless, all images gathered with this kind of set-up from are superimposed by patterns of the X-ray optics. The optics’ capillaries are grouped in hexagonal bundles during the fabrication process and these bundles are grouped together again. This process results in a reduced efficiency in the regions where the bundles are joined making the hexagonal pattern visible. This influence can be removed by the technique of multi-frame super-resolution combining several short measurements with slightly shifted positions. The optics pattern is averaged out and in addition the shifting allows further increase of the lateral resolution. The total measurement time can be kept similar by dividing the single measurement time by the number of “shots” without reducing the sampling size.
This approach of multi-frame super-resolution in combination with a sub-pixel correction algorithm will be illustrated and shown on experimental data. Additionally, a flat-field correction attempt is shown to remove general imaging inhomogeneity. Descriptive image-sets will be presented to demonstrate the potential of such techniques for full-field PIXE imaging [3].
[1] D. Hanf, J. Buchriegler, A. D. Renno, S. Merchel, F. Munnik, R. Ziegenrücker, O. Scharf, S. H. Nowak, J. von Borany, NIM B 377, pp. 17-24 (2016).
[2] S. H. Nowak, A. Bjeoumikhov, J. von Borany, J. Buchriegler, F. Munnik, M. Petric, A. D. Renno, M. Radtke, U. Reinholz, O. Scharf, L. Strüder, R. Wedell, R. Ziegenrücker, X-ray Spectrometry 44 (3), pp. 135-140 (2015).
[3] J. Buchriegler, N. Klingner, D. Hanf, F. Munnik, S. H. Nowak, O. Scharf, R. Ziegenrücker, A. D. Renno, J. von Borany, submitted to Journal of Analytical Atomic Spectrometry (2017)

This work has been supported by BMBF (INTRA r3 033R070) and by Marie Curie Actions - Initial Training Network (ITN) as an Integrating Activity Supporting Postgraduate Research with Internships in Industry and Training Excellence (SPRITE) under EC contract no. 317169.