High bias voltage CZT detectors for high-flux measurements

In this work, we present the performance of new travelling heater method (THM) grown CZT detectors, recently developed at IMEM-CNR Parma, Italy. Thick planar detectors (3 mm thick) with gold electroless contacts on CZT crystals grown by Redlen Technologies (Victoria BC, Canada) were realized, with a planar cathode covering the detector surface (4.1 x 4.1 mm2) and a central anode (2 x 2 mm2) surrounded by a guard-ring electrode. The detectors, characterized by low leakage currents at room temperature (4.7 nA/cm2at 1000 V/cm), allow good room temperature operation even at high bias voltages (> 7000 V/cm). At low rates, the detectors exhibit an energy resolution around 4 % FWHM at 59.5 keV (241Am source) up to 2200 V, by using a commercial front-end electronics (A250F/NF charge sensitive preamplifier, Amptek, USA; nominal equivalent noise charge ENC of 100 electrons RMS). At high rates (1 Mcps), the detectors, coupled to a custom-designed digital pulse processing electronics developed at DiFC of University of Palermo (Italy), show low spectroscopic degradations: energy resolution values of 8 % and 9.7 % FWHM at 59.5 keV (241Am source) were measured, with throughputs of 0.4 % and 60 %, respectively. These activities are in the framework of an Italian research project on the development of energy-resolved photon counting (ERPC) systems for high flux energy-resolved X-ray imaging.