Charge loss correction in CZT pixel detectors at low and high fluxes: analysis of positive and negative pulses

Charge losses are typical drawbacks in cadmium–zinc–telluride (CZT) pixel detectors. The effects of these phenomena are strongly related to the interaction point of the photons and are more severe for photon interactions at the inter-pixel gap and near the pixelated anode. In this work, we present some original techniques able to correct charge losses in pixelated CZT detectors at both low and high fluxes. The height, the shape and the arrival time of collected- and induced-charge pulses with both positive and negative polarities are analysed to recover charge losses after the application of charge sharing addition (CSA). Sub-millimetre CZT pixel detectors, fabricated by different manufacturers (Redlen Technologies, Canada and IMEM-CNR, Italy), are investigated with both uncollimated radiation sources and collimated synchrotron X rays (Diamond Light Source, U. K.), at energies below and above the K-shell absorption energy of the CZT material. The processing of the detector pulses is performed through a digital approach. A 16-channel digital readout electronics was recently developed at University of Palermo (Italy), able to perform on-line multi-parameter analysis (event arrival time, pulse shape, pulse height) and fine coincidence analysis (coincidence time windows < 20 ns). These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for high-flux spectroscopic X-ray imaging (5-150 keV).