Abstract
The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for (224)Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of (224)RaCl(2) 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 (224)Ra) and of the (224)Ra half-life (T(1/2) = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.