Digital CZT Detector System for High Flux Energy-Resolved X-ray Imaging

Photon counting arrays with energy resolving capabilities are recently desired for the next-generation X-ray imaging systems. In this work, we present the performance of a 2 mm thick CZT pixel detector, with pixel pitches of 500 mu m and 250 mu m, coupled to a fast and low noise ASIC (PIXIE ASIC), characterized by only the preamplifier stage. A 16-channel digital readout electronics was used to continuously digitize and process each output channel from the PIXIE ASIC, performing multi-parameter analysis (event arrival time, pulse shape, pulse height) at low and high input counting rates (ICRs). The spectroscopic response of the system to monochromatic X-ray and gamma ray sources, at both low and high ICRs, is presented with particular attention to the mitigation of some typical spectral distortions (pile-up and charge sharing). The detector allows good energy resolution at moderate cooling (3% FWHM 59.5 keV, -1200 V, T = 5 C) by using fast shaped pulses (i.e. pulses with time widths of 300 ns). Charge sharing investigations were performed by using a fine time coincidence analysis (TCA) and a pulse shape analysis (PSA). The potentialities of the PSA for charge sharing detection even at high photon counting rates were also shown.