3-D CdZnTe Gamma-ray Imaging Spectrometers for Nuclear Material Detection and Characterization

Three-dimensional position-sensitive CdZnTe (3-D CZT) detector technology, pioneered by our research group at the University of Michigan, can provide an energy resolution of about 0.50% FWHM at 662 keV, and the position resolution of about 0.3 mm for individual gamma-ray interactions within a single CZT semiconductor crystal. The technological advancements on 3-D CZT detectors have enabled high energy resolution, within a factor of two compared to that of high purity germanium (HPGe) gamma-ray detectors, and gamma-ray imaging capabilities in the entire energy range (from about 20 keV up to 10 MeV). In addition, 3-D CZT detectors are operated at ambient temperatures, without the requirement of cryogenic cooling of HPGe detectors. Therefore, CZT detectors can be turned-on and off instantly without the long cooling time of HPGe detectors before measurement. The combinations of high spectroscopic resolution, high sensitivity, gamma- ray imaging and room temperature operation have made 3-D CZT detectors a new and attractive instrument to detect and characterize radioactive materials in the field. This presentation will introduce the latest research progress at the University of Michigan, including experimental demonstration of the energy resolution approaching 0.30% FWHM at 662 keV on CZT detectors with dimensions of 2x2x1.5 cubic centimeters. This performance is achieved using direct attachment between CZT crystal and the application-specific-integrated-circuitry (ASIC) carrier board to minimize input capacitance, and the deployment of low-noise digital VAD-UM ASICs. It was also demonstrated that an array of 3x3 CZT detectors with a total detection volume of 54 cubic centimeters can detect and locate an 88 Ci Ir-192 source from 600 meters away within just a few minutes. Gammaray images of MOX fuel pins with an imaging resolution of a few mm at Am-241 gamma-ray energy have also been demonstrated at Idaho National Laboratory in August 2017. Applications of 3-D CZT detectors will be summarized. These include monitoring isotope concentration in pipes in nuclear power plants and nuclear facilities over time, radiation imaging in Chernobyl and Fukushima for radiation survey, detecting and characterizing nuclear materials at customs and boarder protection. IAEA Safeguard Division has purchased and evaluated 3-D CZT detectors for safeguard and verification applications. The advantages of 3-D CZT detectors for nuclear security, such as securing radioactive materials, preventing and detecting criminal/unauthorized shipment of radioactive materials, will be discussed. (author)