Benchmarking the repeatability of a pneumatic cyclic neutron activation analysis facility using 16 O(n,p) 16 N for nuclear forensics
A target was prepared for cyclic neutron activation analysis by heat sealing lithium-carbonate in polyethylene. The target was cyclically irradiated 50 times using a Thermo-Scientific accelerator based deuterium–tritium fusion neutron generator. During counting periods, gamma-rays emitted by 16 N were detected using three high-purity germanium detectors acquiring data in list-mode. Total counts acquired in each spectrum were compared between the three detectors to examine variability in geometric positioning of the target and variability of the generator intensity throughout the experiment. These two effects were determined to be the primary sources of variation in the measured counts. Variation in target positioning and generator intensity were found to increase the standard deviation by 34% and 33%, respectively. Transit times to the detector were found to be slower and more variable than transit to the generator but were well below the half second threshold needed to measure short-lived radionuclides with half-lives on the order of seconds. The standard deviation in irradiation time was found to be less than 1 milliseconds. The impact on statistical variability in the measured counts was negligible relative to the two primary sources of variation. Spectra acquired from each cycle were summed together. The sum of the peak areas from the 6.1 MeV gamma-ray and its corresponding single and double escape peaks were used to measure the half-life of 16N. The result of 7.108(15) seconds derived from data suggests that the currently published value of 7.13(2) seconds has minimal systematic bias induced by background.