Capability Demonstration of 3D CdZnTe Gamma-Ray Detectors in Extreme Environments

Abstract

Over the last two decades, advancements in 3D CdZnTe (CZT) gamma-ray detector technology have led to its use in a wide range of applications such as nuclear non-proliferation, defense, nuclear power, environmental monitoring, and medical imaging. Excellent energy resolution, 4-pi Compton imaging capability, and room-temperature operation make 3D CZT detectors ideal for the characterization and localization of radioactive sources. This work aims to explore the feasibility of operating CZT in tougher, more challenging environments and in applications with stringent requirements in terms of the detector’s stability, power consumption, weight, and size. The effects of extreme ambient temperatures, neutron damage, and space-like environments were investigated to help benchmark and advance the capabilities of CZT detector technology.

Removal of the temperature regulation used to keep CZT at room temperature can help minimize the power consumption, weight, and size of detector systems. However, this also introduces some technical challenges, as the behavior of CZT detector systems at extreme temperatures is not yet well understood. Temperature-related effects were studied for several 3D CZT detectors for ambient temperatures ranging from 20 degrees Celsius to 60 degrees Celsius. Detector leakage increases exponentially with temperature, making operation more difficult. Nonetheless, it was demonstrated that with minor adjustments, not only is operation at 60 degrees Celsius possible, but satisfactory energy resolution can still be achieved without any active temperature regulation. Issues were identified and resolved to help minimize the degradation of performance at high temperatures. Also, decreased efficiency for some detectors below room temperature (-10 degrees Celsius) was investigated and found to be related to distortions in the detector’s internal electric field. The effect of annealing on CZT detectors with and without neutron damage was explored. Annealing at 80 degrees Celsius improved the quality of several detectors without previous radiation damage and helped recover performance for CZT detectors exposed to a neutron fluence of 1E12 neutrons per square centimeter. Nonuniformity of neutron damage and unexpected instability over time was further studied.

Gamma-ray detectors can be useful in space applications such as planetary science; however, the 3D CZT technology developed at the University of Michigan has not yet been space-qualified. In collaboration with Los Alamos National Laboratory, a 3D CZT detector system, Orion Eagle, was specifically designed for near-space environments. Orion Eagle was integrated into a gondola and launched on a NASA high-altitude balloon. The detector measured atmospheric radiation during a 9 h flight reaching a float altitude of nearly 40 km, verifying the effectiveness of the design and demonstrating the first successful operation of this technology in a near-space environment. The dataset obtained from the flight was used to develop algorithms to discriminate between gamma-ray and cosmic ray interactions in the CZT detector. Overall, this work led to a greater understanding of fundamentals related to 3D CZT performance in extreme environments, which is essential for guiding the development of future detector systems.