Two determinations of the 223Ra half-life

Ra-223 is an alpha-emitter that is being used as a bone-seeking radiotherapeutic agent. The relatively large uncertainty on its evaluated half-life (0.26%, Bé et al., 2011) is an impediment to precision activity assays, which often involve measurements by various methods over time spans of days or weeks. We have performed two series of measurements using an ionization chamber (IC) and a NaI(Tl) well counter (γ-wc) to determine new, precise values for the 223Ra half-life. We have endeavored to realistically assess the uncertainties on the derived half-lives, looking beyond the fit uncertainties to identify uncertainty components acting on multiple timescales. We recovered respective values of 11.447(6) d and 11.445(13) d from the IC and γ-wc measurements. Our values are in accord with the evaluated value of 11.43(3) d, but with smaller combined uncertainties.