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Full-field PIXE imaging: Multi-frame super-resolution to overcome optics pattern and imaging-based resolution limitations
Buchriegler, J.ORC; Klingner, N.ORC; Munnik, F.; Nowak, S. H.ORC; von Borany, J.; Ziegenrücker, R.
The combination of a pnCCD-based detector (264 x 264 pixels) with a polycapillary 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, flat/polished geological samples with respect to their (trace) elemental composition. In the standard configuration a 1:1 polycapillary X-ray optics (78 mm length, 20 µm capillary diameter) is used to guide the emitted photons towards the pnCCD-chip divided into nearly 70000 pixels. Their dimensions of 48 x 48 µm² cause a native lateral resolution of about 100 µm. By applying dedicated sub-pixel algorithms to recalculate the footprint of the photon’s electron cloud in the chip [2], this limitation can be bypassed and the lateral resolution is then mainly determined by the capillary’s diameter.
Nevertheless, all images gathered with this kind of set-up from a single measurement are superimposed by the optics pattern. 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 transparency in the regions where the bundles are joint making the hexagonal pattern visible. This influence can be (largely) removed by combining several short measurements with slightly shifted positions. The optics pattern is averaged out and in addition the lateral information (shift-lengths) can be used to further improve the resolution limit beyond the pixels’/capillaries’ dimensions. The total measurement time can be kept almost similar by dividing the single measurement time by the number of “shots” without losing statistics/sensitivity.
Results from descriptive image-sets of first test-measurements will be shown to demonstrate the potential of this technique for full-field PIXE imaging.

[1] D. Hanf et al., NIM B, Vol. 377, pp. 17-24 (2016).
[2] S.H. Nowak et al., X-ray Spec., Vol. 44 (3), pp. 135-140 (2015).
Keywords: full-field imaging, capillary optics, super resolution
  • Lecture (Conference)
    15th International Conference on Particle Induced X-ray Emission, 02.-07.04.2017, Split, Croatia

Publ.-Id: 24934 - Permalink