Primary and secondary activity standards for ⁸⁹Zr

NIST recently completed a primary standardization using Triple-to-Double Coincidence Ratio (TDCR) liquid scintillation counting as the primary method. CIEMAT/NIST efficiency tracing was performed as a confirmation. As previously reported by the Physikalisch-Technische Bundesanstalt (PTB) in Germany, combined standard uncertainties are larger than usually encountered, 0.79% for TDCR, with large components between filters and between scintillants. Sources with a range of volumes were measured. Detector-specific Monte Carlo modelling of the backscatter correction led to improved performance of the model over the range of volumes. Secondary standards were determined for a 5 mL solution in a NIST-1 type ampoule for the NIST secondary standard ionization chambers, a Vinten ionization chamber, and Capintec commercial radionuclide calibrators. In addition, secondary standards were determined for a 4 mL solution in a 10R vial, adding indirect comparisons to previous standardizations at the National Physical Laboratory (NPL) in the United Kingdom. Finally, secondary standards were developed for a 2 mL solution in an ISO 10R vial and a 1 mL solution in a 3 mL plastic syringe.