Determination of the Fast Fission Yield of Praseodymium-141 by Neutron Activation Analysis

Praseodymium-141 (stable) is a potentially useful burnup monitor for both fast and thermal reactor fuels. The fission yield is high, the half lives of its volatile precursors are short, and it is not a constituent of virgin or reprocessed fuels. However, neither the fast nor the thermal fission yield of this isotope has 'been measured. Of the various analytical techniques which have been used previously to determine fission yields, e. g., mass spectrometry, spectrophotometry, and radiochemistry, none is applicable to the determination of praseodymium-141. Thermal yields of the parent nuclide cerium-141 (31 days) have been published, but uncertainties in the decay scheme of cerium-141 and inaccuracies in establishing the number of fissions which produced this cerium nuclide make the values questionable. Neutron activation followed by gamma spectrometry, a technique that affords a means of high sensitivity and high specificity, is presently being investigated (ANL-7125, p. 242) for the determination of the fission yield of praseodymium-141.