Primary Standardization Of Ra-224 Activity By Liquid Scintillation Counting

A standard for activity of Ra-224 in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4 pi alpha beta(LS)-gamma(NaI(Tl)) anticoincidence counting, as well as by 4 pi gamma ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators).