Large Volume CdZnTe Radiation Detectors

Gamma-ray imaging spectrometers based on three-dimensionally position-sensitive CdZnTe detectors have been adopted globally by many scientists for stockpile stewardship and nuclear safeguards. These detection systems have been selected for their ability to accurately measure special nuclear materials in a convenient form factor, at a competitive price point, with smaller size, weight, and power requirements than alternative sensors. High-purity germanium detectors have been employed for many measurements within the nuclear security complex. However, high-purity germanium must be cooled to cryogenic temperatures for more than twenty-four hours prior to measurements, which can make mobile deployment challenging. CdZnTe detectors can be configured into more compact designs without any power consumption for active cooling. The inherent ability of CdZnTe sensors to form gamma-ray images allows operators to “see” radiation hazards or map the configuration of radioactive materials inside an object. The main disadvantages of commercially available CdZnTe systems are that they are not as efficient as typical high-purity germanium detectors, and that the cost to fabricate more efficient CdZnTe does not scale well due to poorer material yield. This Phase I effort is a collaboration between a premier CdZnTe crystal grower and a CdZnTe product developer, who has effectively delivered valuable spectroscopy and imaging solutions to the nuclear security complex and other global customers. These collaborators will work together to grow large-volume CdZnTe sensors with dimensions of 4.4 x 4.4 x 1.5 cm3 , a significant increase from the standard format of 2.2 x 2.2 x 1 cm3 . These larger sensors will be much more efficient, especially for high-energy photons, than existing product offerings. They will be inherently more rugged due to the elimination of packaging challenges faced when arraying smaller sensors into products and will not have gaps between detector elements, which will improve the signalto-noise ratio of certain imaging modalities. Furthermore, these sensors will have a significantly reduced cost per unit volume compared with previous iterations of thicker CdZnTe sensors, reducing cost by nearly a factor of two due to novel detector processing selections. The project collaborators are equipped to evaluate the quality of these new sensors due to many years of experience testing CdZnTe and the deployment of new, pulse-waveform sampling application specific integrated circuits which provide extensive information about charge drift in the CdZnTe detectors. This information can be used to iterate the production processes to reduce the formation of space charge or charge trapping centers and reduce non-uniformities in electric field. Commercially, the result of this Phase I and Phase II development will be a new, marketable detector configuration to be used in already successful products. This new configuration will enable higher efficiency detection of high-energy gamma rays in a room temperature, rugged sensor platform with excellent energy resolution and enhanced gamma-ray imaging performance.