Digital performance improvements of a CdTe pixel detector for high flux energy-resolved X-ray imaging

Photon counting detectors with energy resolving capabilities are desired for high flux X-ray imaging. In this work, we present the performance of a pixelated Schottky Al/p-CdTe/Pt detector (4×4) coupled to a custom-designed digital readout electronics for high flux measurements. The detector (4×4×2 mm3) has an anode layout based on an array of 16 pixels with a geometric pitch of 1 mm (pixel size of 0.6 mm). The 4-channel readout electronics is able to continuously digitize and process the signals from each pixel, performing multi-parameter analysis (event arrival time, pulse shape, pulse height, pulse time width, etc.) even at high fluxes and at different throughput and energy resolution conditions. The spectroscopic response of the system to monochromatic X-ray sources, at both low and high rates, is presented with particular attention to the mitigation of some typical spectral distortions (pile-up, baseline shifts and charge sharing). At a photon counting rate of 520 kcps/pixel, the system exhibits an energy resolution (FWHM at 59.5 keV) of 4.6%, 7.1% and 9% at throughputs of 0.9%, 16% and 82%, respectively. Measurements of Ag-target X-ray spectra also show the ability of the system to perform accurate estimation of the input counting rate up to 1.1 Mcps/pixel. The aim of this work is to point out, beside the appealing properties of CdTe detectors, the benefits of the digital approach in the development of high-performance energy resolved photon counting (ERPC) systems for high flux X-ray imaging.