Improving Cadmium Zinc Telluride Spectrometer Performance and Capabilities.

Abstract

CdZnTe is the premier semiconductor material for room-temperature gamma-ray spectroscopy and imaging. The high effective atomic number of 52 and high density of 6 grams per centimeter cubed yield excellent detection efficiency; a pixelated detector design allows for 3D position sensitivity and material non-uniformity corrections resulting in <1% FWHM energy resolution at 662 keV; the wide bandgap of 1.61 eV permits room temperature operation. Fabrication improvements and the feasibility of floating-temperature operation are analyzed in this work.

Several fabrication changes are tested to mitigate gain nonuniformity in some pixels during operation. Changing the substrate from printed circuit board to ceramic improves operation, maintains spectroscopic performance, and is adopted. Switching the electrode contacts from gold to platinum drastically raises the leakage current and is rejected. Two proprietary fabrication techniques are proposed. The first, fabrication A, raises the leakage, degrades spectroscopic performance, and is rejected. The second, fabrication B, causes greater gain nonuniformity, degrades resolution, and is also rejected.

To reduce system power consumption, a temperature correction algorithm is developed that allows data collection at operating temperatures different from the calibration temperature without performance degradation. This begins with isolating the temperature effects to the detector rather than the readout electronics, and demonstrating the accuracy of the electronic baseline as a surrogate for temperature. Considering the temperature effects, linear gain corrections only partially recover spectroscopic performance and cannot account for pixel nonuniformity or energy nonlinearity.

Parametric corrections pinpoint specific aspects of system operation susceptible to change with temperature. Peak hold drop, depth of interaction, and gain as a function of depth are individually corrected and recover spectroscopic performance almost entirely. To reduce data requirements, the corrections are reapplied assuming separability between the temperature and original parameter domains, with minimal resolution degradation.