Systematic uncertainties in high-rate germanium data

• Published in: 2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) pp. 1 - 3
• Main Authors: Gilbert, Andrew J., Fast, James E., Fulsom, Bryan G., Pitts, W. Karl, VanDevender, Brent A., Wood, Lynn S.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.10.2015
• Subjects: Cooling; Detectors; Energy resolution; Fuels; Isotopes; Systematics; Uncertainty
• DOI: 10.1109/NSSMIC.2015.7581931

For many nuclear material safeguards inspections, spectroscopic gamma detectors are required which can achieve high event rates (in excess of 10 6 s -1 ) while maintaining very good energy resolution for discrimination of neighboring gamma signatures in complex backgrounds. Such spectra can be useful for non-destructive assay (NDA) of spent nuclear fuel with long cooling times, which contains many potentially useful low-rate gamma lines, e.g., Cs-134, in the presence of a few dominating gamma lines, such as Cs-137. Detectors in use typically sacrifice energy resolution for count rate, e.g., LaBr 3 , or vise-versa, e.g., CdZnTe. In contrast, we anticipate that beginning with a detector with high energy resolution, e.g., high-purity germanium (HPGe), and adapting the data acquisition for high throughput will be able to achieve the goals of the ideal detector. In this work, we present quantification of Cs-134 and Cs-137 activities, useful for fuel burn-up quantification, in fuel that has been cooling for 22.3 years. A segmented, planar HPGe detector is used for this inspection, which has been adapted for a high-rate throughput in excess of 500k counts/s. Using a very-high-statistic spectrum of 2.4 × 10 11 counts, isotope activities can be determined with very low statistical uncertainty. However, it is determined that systematic uncertainties dominate in such a data set, e.g., the uncertainty in the pulse line shape. This spectrum offers a unique opportunity to quantify this uncertainty and subsequently determine required counting times for given precision on values of interest.