Standardisation of ²²³Ra by liquid scintillation counting techniques and comparison with secondary measurements

An aqueous solution of ²²³Ra chloride in equilibrium with its decay progeny was standardised by liquid scintillation counting techniques. Since secular equilibrium with the decay progeny of ²²³Ra had been established by the time of measurement, the apparent detection efficiency of ²²³Ra was approximately 6 and was determined by both the CIEMAT/NIST efficiency tracing technique and the 4π(LS)-γ digital coincidence counting techniques. The results obtained were compared with γ-spectrometry and ionisation chamber measurements. Whilst the γ-spectrometry measurements were in agreement (albeit exhibiting a large spread (18%) in the individual activity estimations using the main γ-emissions), a significant discrepancy of the order of 9% was identified between the liquid scintillation counting results and those obtained using published calibration factors for a variety of radionuclide calibrators.