A linear array of position-sensitive virtual Frisch-grid CdZnTe for low-energy gamma rays

Large-area arrays of position-sensitive virtual Frisch-grid CdZnTe (CZT) detectors with enhanced energy resolution and high efficiency have been proposed for spectroscopy and imaging of gamma-ray sources. Here, we present the design and test results of a linear array of such detectors optimized for use in handheld instruments. There are several application areas for such detectors including uranium enrichment measurements, storage monitoring, dosimetry and other nuclear safeguards related tasks. The array configuration provides a large area with minimum number of readout channels, which potentially allows the developers to avoid using ASIC-based readout electronics by substituting it with hybrid preamplifiers followed by digitizers. The array prototype consists of 6 5×7×25 mm3 CZT detectors side-oriented with respect to the source to achieve the maximum area. Each detector is furnished with 5 mm-wide charge-sensing pads placed near the anode. As an option, the pads can be grouped together to reduce the number of readout channels. The same can be done with the cathodes. The pads signals are converted into X-Y coordinates and combined with the cathode signals (for the Z coordinates) to give 3D positional information of each interaction point. This information is used to correct the response non-uniformity caused by material inhomogeneity, which allows the developers to use standard grade (unselected) CZT crystals, while retaining high spectroscopic performance.