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The presented work describes the capabilities of a state-of-the-art spectroscopic photon-counting hybrid pixel detector for use in non-destructive testing, as a contaminant detector with potential uses in the food and pharmaceutical industries. A pharmaceutical hard capsule containing vitamin powder, contaminated with Steel (ST) and Tungsten (W) was prepared under controlled conditions. Both contaminants are distinguished from the powder by combining sub-pixel imaging with spectroscopic imaging analysis, made possible by the use of a 2 mm CdZnTe sensor coupled to a Timepix3 ASIC, operated in Time-over-Threshold and Time-of-Arrival mode. The sub-pixelization technique achieves a spatial resolution of 18.3 μm, with a maximum photon flux of 2.5× 106 photons/s· cm2. For the spectral analysis technique implemented, each energy bin image is energy-weighted, with weights optimally defined by considering the bin contrast and noise behavior, and combined to form an integrated-spectrum enhanced image with increased contaminant visibility. Contrast-to-Noise Ratio (CNR) for each contaminant type was used for performance assessment of the approach. A CNR increase of 106% above the reference unweighted-spectrum image was achieved for the ST contaminant, while the denser W contaminant showed a CNR increase of 80%. This means that the presented spectroscopic imaging technique is feasible for implementation in material visibility enhancement.

A: X-ray imaging techniques that distinguish radiation in different energy ranges offer the advantage of material differentiation based on the material-specific properties of the object to be examined. One possibility to obtain spectroscopic information is the K-edge approach utilizing energy thresholds. A basic information about the photon energy is needed for this purpose. The Medipix3RX is a photon-counting semiconductor detector which provides multiple energy thresholds in a single recording and so an energy information. It offers up to eight independent energy thresholds per pixel with high spatial and high energy resolution. In order to investigate the possibility of material discrimination by X-ray imaging methods with Medipix3RX detectors, an absorption phantom was fabricated and examined which consists of 8 different materials in various thicknesses. For material separation the K-edge method was used, which exploits the abrupt rise of photo absorption for energies above the ionization energy of electrons in the atomic K-shell. After performing a threshold equalization and a threshold-energy calibration of the detector, X-ray images were taken of the phantom. After evaluation, five of the eight materials of the phantom were successfully separated and identified with the selected settings of the X-ray tube. These include gadolinium and iodine, which are used as contrast agents in oncology. The most reliable material discrimination was achieved for tungsten and gadolinium. Due to their high K-edge energy, they had the greatest influence on the spectrum used. Elements with a low atomic number, however, could be distinguished less confidently due to the low photo absorption in the energy spectrum used and the resulting low effect on the change of the measured total intensity. This article describes the experimental setup of the energy calibration and X-ray image analysis of a Medipix3RX detector with a 1 mm CdTe sensor as well as the performance and evaluation of these and shows first results in material identification with eight energy thresholds in spectroscopic single pixel mode configuration.

In this work, different Cadmium Telluride (CdTe) sensor configurations are assessed for the usage in a robot assisted portable gamma camera. In the first part, four CdTe sensors, with thickness of 0.45 mm, 1 mm, 2 mm and 3 mm and pixel sizes of 55 µm and 110 µm, are investigated regarding their spectroscopic performance. The photon counting detector Timepix1 is hereby used. The 3 mm CdTe sensor shows increase in count rate up to a factor of 1.25 compared to a 2 mm CdTe sensor, 1.84 compared to a 1 mm CdTe sensor and up to 2.71 compared to a 0.45 mm CdTe sensor in the case of 137 Cs. In the second part, the 3 mm CdTe sensor was implemented in a commercially available gamma camera, the iPIX. The system was integrated in the bomb disposal robot and tested in different scenarios. The integrated 3 mm CdTe detector measured 21.5 counts per second emitting from a 60 Co source with an activity of 2.8 ± 0.07 Gbq in 20 meters distance in an open environment. The acquisition time was 116 seconds. The angular resolution was sufficient for the user to localize the radioactive isotope inside the test structure.