Preparation and calibration of a 231 Pa reference material

A Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of Pa tracers produced for U- Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified Pa solution using a Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the Pa spike solution to decay to U and then measuring the ingrown U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new Pa reference material will simplify calibration of the Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages.