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

One of the most commonly-used methods for determination of Ra-226, 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 Ra-228 using the same source. The adaptations presented here do not introduce any contaminants that will affect the separation of radium or alpha counting for Ra-226, and can be used for re-analysis of already existing sources prepared by BaSO4 co-precipitation. The first adaptation uses detection of Ac-228 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 Ac-228 grows in quickly, taking less than 2 days to reach equilibrium with the Ra-228 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 Th-228 activity. Although ingrowth periods for Th-228 can be lengthy, very low detection limits for Ra-228 can be achieved with this technique. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved,