CdZnTe gamma-ray spectroscopy in high flux environments using digital pulse processing techniques

Abstract

CdZnTe imaging gamma-ray spectrometers using digital pulse processing techniques have shown great promise in recent years. The energy resolution of 15 mm thick CdZnTe spectrometers has improved to around 0.4 % FWHM at 662 keV for single pixel events and near 0.6 % FWHM at 662 keV using all events, regardless of the number of pixels triggered. Additionally, the position resolution through subpixel position sensing has improved to less than 300 μm FWHM for 662 keV gamma-rays. This technical progress has encouraged the use of CdZnTe in challenging environments with high gamma ray fluxes such as nuclear power plants. CdZnTe is also being studied for use in medical imaging applications as well as nuclear safeguards and treaty verification where high count rate environments may be encountered. Signal pulse waveforms generated from charge motion in CdZnTe were studied at high count rates to learn how the material responds in high gamma-ray fluxes. The relationship between average preamplifier decay slope and dose rate is shown to be monotonic. This relationship could be used in a real system to estimate the dose rate on the detector surface. Minimal energy resolution degradation was observed up to 50 mR/hr. Beyond 50 mR/hr, the energy resolution degrades more substantially for multiple pixel events due to chance coincidence Compton scattering events. Changes in the electric field due to positive space charge accumulation were observed which likely contributes to the energy resolution degradation. Preamplifier instability is the other major contributor to energy resolution degradation.