Adaptation of Pixelated CdZnTe gamma-ray imaging technology for in situ planetary science applications

It is important for planetary sciences to find a gamma-ray spectrometer that is compact, light and provides good energy resolution in an energy range that varies from ~ 30 keV to 10 MeV. Pixelated CdZnTe detector is a good candidate for this application due to its small volume, light weight and it has demonstrated good energy resolution below ~2-3 MeV. At higher energies, charge sharing effect becomes a problem due to the size of the pixel. In this paper, the electron cloud diameter as a function of energy has been studied using the MCNPX Monte Carlo code. In the energy range studied, the electron cloud size increases linearly with energy. The effect of charge sharing in a 2×2×1.5 cm
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pixelated CdZnTe detector at 662 keV, 2.614 MeV and 7.631 MeV is shown. The anode is an 11 × 11 pixelated array with 1.72 mm pitch. The simulation reveals that the electron cloud size is about three times the size of the pixel pitch for an 8 MeV event. As the energy of the source increases, charge sharing effect is dominant and the charge cloud is collected by multiple pixels which reduces the spectral performance of the detector.