High-Resolution 3D CdZnTe Drift Strip Detectors for Astrophysical and Medical Applications

Abstract

During the past 20 years, three-dimensional (3D) cadmium-zinc-telluride (CZT) detectors have seen significant advancements in room-temperature gamma-ray spectroscopic imaging. Recently, in the framework of a collaboration between Italian research groups, novel spectroscopic gamma-ray imaging systems, based on high-resolution CZT drift-strip detectors, were developed. The detectors are equipped with orthogonal strips in the anode and cathode electrodes, working as collecting anode strips and drift strips, negatively biased to enhance charge collection. The cross-strip electrode patterns of cathode/anode electrodes allow 2D positioning, while the third coordinate is provided by the cathode/anode signal ratio. This detector design ensures fewer read-out channels in comparison with 2D pixelated detectors. A custom high-performance digital read-out electronics was used in order to acquire and analyse the wide range of collected and induced charge pulse shapes. The 3D CZT drift-strip detectors were treated by using a novel surface passivation technique, ensuring extremely low leakage currents between the drift strips and allowing the use of high-drift bias voltages with significant improvements in charge collection and energy resolution. The detectors showed excellent room-temperature energy resolution (1.3% FWHM at 662 keV) without spectral corrections. Through a novel correction technique based on the analysis of collected/induced charge pulses from anode and drift strips, further improvements (0.8% FWHM at 662 keV) were also achieved. These activities are within two Italian research projects aiming for the development of spectroscopic gamma-ray imagers in the energy range of 10-1000 keV for astrophysical and medical applications (3DCaTM and 3CaTS projects, financed by ASI and INFN, respectively). A novel single-photon emission computed tomography (SPECT) system for real-time therapeutic dose monitoring in binary hadron therapy (boron neutron capture therapy (BNCT)) was developed as part of the 3CaTS project. The goal of the 3DCaTM project is to develop a detection system that can simultaneously perform spectroscopy (10-1000 keV), imaging, timing, and polarimetric scattering on a space telescope using new high-energy optics (like a broadband Laue lens), as well as small wide-field instruments to be used on clusters of micro-satellites.