Performance evaluation of a European scale proficiency test on radon-in-water measurements in Europe

In 2018, a Europe wide proficiency test (PT) on measurements of the massic activity of ²²²Rn in drinking water was organised with the participation of 101 European environmental radioactivity monitoring laboratories. The performance of the participating laboratories was evaluated by comparing submitted results to the reference value using percentage deviation, z-score and zeta-score. It was found that 84% of the participants' results were within the ±20% reference range. When analysing the zeta-score it was found that 76% of the participants' results were acceptable. The accompanied questionnaire and workshop helped to identify practices that could lead to erroneous results. As it was probably the largest scale PT on radon-in-water ever, the evaluation of results is representative of the quality of radon-in-water monitoring in the EU today.