Evaluation of the Spectroscopic Performance of 3D CZT Drift Strip Detectors

CdTe/CZT is an attractive and consolidated material with which to realize detectors with good efficiency and energy resolution, operating at room temperature and suitable for a large variety of applications such as medical imaging, nuclear security, and astrophysics. Right in this last field several spectro-imagers based on these CdTe/CZT detectors were mounted onboard space missions such as INTEGRAL, Swift, and NuSTAR for hard X and gamma-ray astrophysics. Much effort has been expended in the development of CZT spectroscopic imagers for obtaining sub-millimeter spatial resolution in three dimensions (3D) and high energy resolution up to 1 MeV. The motivations are mainly related to the possibility to perform simultaneous measurements of energy, timing, and 3D positioning of X and gamma rays. This kind of 3D detector is particularly suitable to realize scattering polarimeters and Advanced Compton detectors. In this paper, we present the performance of high-resolution CZT drift strip detectors, recently realized at IMEM-CNR (Parma, Italy) in collaboration with due2lab company (Scandiano, Italy). The detectors are operated in the Planar Transverse Field (PTF) configuration, in which photons hit the detector orthogonally to the direction of the electric field established between the two electrodes, as well as in the standard configuration. They are able to determine the 2D position thanks to the strips deposited on electrodes orthogonally, while the third coordinate is derived from the Cathode/Anode ratio and/or drift time. We report the experimental results in terms of energy resolution, peak-to-valley ratio, threshold, and gain, as well as charge collection efficiency for 2 different samples and several energies of calibration. We also report the results obtained by using a novel correction technique based on the analysis of collected-induced charge pulses from anode and drift strips.