Radon leakage as a source of additional uncertainty in simultaneous determination of 226Ra and 228Ra by gamma spectrometry—Validation of analysis procedure

•226Ra and 228Ra determined gamma spectrometrically via 214Pb and 228Ac.•Procedure proved to be robust for conserved water samples of pH <3.•Uncertainty component due to variations in Rn leakage estimated to be 6.5%.•Needs to be considered when 226Ra is determined via progeny in similar matrices.•Results of an intercomparison study proved the procedure to be fit for its purpose.

A series of validation experiments was carried out to assess robustness, repeatability, and trueness of an analysis procedure for simultaneous determination of 226Ra and 228Ra in water samples. The study revealed instabilities in the radon holding capacity of the sample matrix (epoxy resin). The discovered effect is a new additional component in the uncertainty budget which should be considered when 226Ra is measured via its progeny in similar sample matrices.