title: Revision of the NIST Standard for (223)Ra: New Measurements and Review of 2008 Data.
abstract: After discovering a discrepancy in the transfer standard currently being disseminated by the National Institute of Standards and Technology (NIST), we have performed a new primary standardization of the alpha-emitter (223)Ra using Live-timed Anticoincidence Counting (LTAC) and the Triple-to-Double Coincidence Ratio Method (TDCR). Additional confirmatory measurements were made with the CIEMAT-NIST efficiency tracing method (CNET) of liquid scintillation counting, integral γ-ray counting using a NaI(Tl) well counter, and several High Purity Germanium (HPGe) detectors in an attempt to understand the origin of the discrepancy and to provide a correction. The results indicate that a -9.5 % difference exists between activity values obtained using the former transfer standard relative to the new primary standardization. During one of the experiments, a 2 % difference in activity was observed between dilutions of the (223)Ra master solution prepared using the composition used in the original standardization and those prepared using 1 mol·L(-1) HCl. This effect appeared to be dependent on the number of dilutions or the total dilution factor to the master solution, but the magnitude was not reproducible. A new calibration factor ("K-value") has been determined for the NIST Secondary Standard Ionization Chamber (IC "A"), thereby correcting the discrepancy between the primary and secondary standards.
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: B E
authors.initials: BE
authors.lastname: Zimmerman
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: D E
authors.initials: DE
authors.lastname: Bergeron
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: J T
authors.initials: JT
authors.lastname: Cessna
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: R
authors.initials: R
authors.lastname: Fitzgerald
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: L
authors.initials: L
authors.lastname: Pibida
keywords: anticoincidence counting; ionization chambers; liquid scintillation spectrometry; radium-223; standards; traceability