Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison

• Published in: Applied radiation and isotopes 2021-04, Vol.170, p.109572-109572, Article 109572
• Main Authors: Bergeron, Denis E., Collins, Sean M., Pibida, Leticia, Cessna, Jeffrey T., Fitzgerald, Ryan, Zimmerman, Brian E., Ivanov, Peter, Keightley, John D., Napoli, Elisa
• Format: Article
• Language: English
• Subjects: Activity standard; Alpha therapy; Coincidence counting; Comparison; Decay constant; Emission probability; Gamma-ray spectrometry; Ionization chamber; TDCR
• ISSN: 0969-8043; 1872-9800
• DOI: 10.1016/j.apradiso.2020.109572

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 (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations. •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 Iγ = 4.011(16) per 100 disintegrations of 224Ra.•The 224Ra half-life is evaluated as T1/2 = 3.6313(14) d.