Validation of a method for measuring radon-222 in water using two-phase liquid scintillation counting according to the ISO/IEC 17025 criteria

A method for measuring radon-222 in drinking water by liquid scintillation counting has been validated according to the ISO/IEC 17025 criteria. A two-phase counting method based on ISO 13164-4 was selected. The counting parameter settings were studied for two water-immiscible cocktails, namely Mineral Oil Scintillator and Opti-Fluor O. Validation of the method includes repeatability, accuracy, uncertainty and detection limit. In order to ensure the validity of the results, internal quality controls should be used and trends analysed. These include background and efficiency control, and precision and accuracy determination. Furthermore, regular participation in interlaboratory comparisons or proficiency-testing programmes are essential.