New Results on High-Resolution 3-D CZT Drift Strip Detectors

Intense research activities have been carry out in the development of room temperature gamma ray spectroscopic imagers, aiming to compete with the excellent energy resolution of high-purity germanium (HPGe) detectors (0.3 % FWHM at 662 keV) obtained after cryogenic cooling. Cadmium-zinc-telluride (CZT) detectors equipped with pixel, strip and virtual Frisch-grid electrode structures represented an appealing solution for room temperature measurements. In this work, we present the performance of new high-resolution CZT drift strip detectors (19.4 x 19.4 x 6 mm3), recently fabricated at IMEM-CNR of Parma (Italy) in collaboration with due2lab company (Reggio Emilia, Italy). The detectors, working in planar transverse field (PTF) irradiation geometry, are able to perform 3D positioning and energy measurement of X rays and gamma rays: 2D positioning through cross-strip electrode patterns on the cathode/anode electrodes and the third coordinate by exploiting the C/A ratio and/or the drift time. A 32-channel digital electronics was used to process and analyze the zoo of collected/induced charge pulses from the strips. Excellent room temperature energy resolution (0.9 % FWHM at 662 keV) characterizes the detectors, after the application of a new correction technique. These activities follow the goals of two Italian research projects (3DCaTM and 3CaTS projects funded by ASI and INFN, respectively) on the development of spectroscopic X-ray and gamma ray imagers (10 keV-1 MeV) for medical and astrophysical applications.