²²⁸Ra and ²²⁶Ra measurement on a BaSO₄ co-precipitation source

One of the most commonly-used methods for determination of ²²⁶Ra, particularly in water samples, utilises co-precipitation of Ra with BaSO₄, followed by microfiltration to produce a source for alpha counting. This paper describes two extensions to BaSO₄ co-precipitation methods which enable determination of ²²⁸Ra using the same source. The adaptations presented here do not introduce any contaminants that will affect the separation of radium or alpha counting for ²²⁶Ra, and can be used for re-analysis of already existing sources prepared by BaSO₄ co-precipitation. The first adaptation uses detection of ²²⁸Ac on the source by gamma spectrometry. The detection efficiency is high, allowing analysis of water samples at sufficiently low activity to be suitable in testing for compliance with drinking water quality standards. As ²²⁸Ac grows in quickly, taking less than 2 days to reach equilibrium with the ²²⁸Ra parent, this can also be useful in radiological emergency response situations. The second adaptation incorporates a method for the digestion of BaSO₄ sources, allowing separation of thorium and subsequent determination of ²²⁸Th activity. Although ingrowth periods for ²²⁸Th can be lengthy, very low detection limits for ²²⁸Ra can be achieved with this technique.