[en] A ²³¹Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of ²³³Pa tracers produced for ²³⁵U-²³¹Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified ²³¹Pa solution using a ²³³Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the ²³³Pa spike solution to decay to ²³³U and then measuring the ingrown ²³³U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new ²³¹Pa reference material will simplify calibration of the ²³³Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages. (author)

[en] A ²³¹Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of ²³³Pa tracers produced for ²³⁵U–²³¹Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified ²³¹Pa solution using a ²³³Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the ²³³Pa spike solution to decay to ²³³U and then measuring the ingrown ²³³U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new ²³¹Pa reference material will simplify calibration of the ²³³Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages.

[en] Highlights: • NIST and NPL activity standards for ²²⁴Ra are demonstrated to be in accord. • The absolute emission intensity for the 241 keV γ ray is evaluated as I_γ = 4.011(16) per 100 disintegrations of ²²⁴Ra. • The ²²⁴Ra half-life is evaluated as T_1/2 = 3.6313(14) d. The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for ²²⁴Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of ²²⁴RaCl₂ were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (I_γ = 4.011(16) per 100 disintegrations of ²²⁴Ra) and of the ²²⁴Ra half-life (T_1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.