CdZnTe Position-sensitive Drift Detectors for Spectroscopy and Imaging of Gamma-ray Sources

CdZnTe (CZT) is an attractive detecting medium for fabricating room-temperature operating gamma-ray detectors, which have a wide range of applications including nonproliferation, safeguards, national security, medical imaging and astrophysics. Virtual Frisch-grid (VFG) CZT detectors operate like classic gas ionization chambers with virtual Frisch-grids, in which the electron clouds generated by the incident photons drift in the external electric field towards the collecting electrode and generate output signals used for spectral analysis of the detected photons. The performance of CZT detectors depends on how efficiently the electron clouds can be transported from the interaction points to the collecting electrodes. The carriers generated in the ionization process could be trapped by crystal defects, which can be present at high concentrations in CZT. Recently we demonstrated a technique that allows us to correct the inhomogeneity in the response of CZT materials by employing high-granularity position-sensitive detector designs. The position-sensing technique allows for segmenting the detectors’ volumes into large numbers of small “virtual” voxels and normalizing the responses generated by the incident photons in each of them. Arrays of such detectors can be integrated into compact hand- held instruments for many practical applications, such as international safeguards, nonproliferation, arms control, and homeland security. In this work, we will report the results from testing small arrays of CZT position-sensitive drift detectors and discuss the effective integration of such arrays with low-noise electronics into a compact hand-held instrument for potential use in safeguards measurements by IAEA inspectors. The work to develop a compact radiation detection instrument for safeguards measurements was supported by the U. S. Department of Energy, Office of Nonproliferation and International Security, Office of Nuclear Safeguards & Security, Next Generation Safeguards Initiative’s Safeguards Technology Development Team (NA-241), and the work to develop CZT detectors with thickness up to 50 mm was supported by the U. S. Department of Energy, Office of Defense Nuclear Nonproliferation Research & Development (NA-22).