Radon measurements in soil: comparative analysis of the first four Italian national intercomparisons

Radon in soil is a key factor for evaluating the potential for indoor radon exhalation, and it is important in environmental and geophysical research. To ensure consistency in measurements among laboratories and assess method performance, national inter-laboratory comparisons (ILCs) on radon-in-soil concentration—called IRSOIL—have been conducted annually in Italy since 2021. In the first four ILCs, 39 measurement spots across six locations with different geological and environmental characteristics were examined. Participants used active sampling techniques in accordance with ISO 11665-11, and the results were statistically analysed using robust estimators, as outlined in ISO 13528. Performance indicators showed that 87% of z-scores and 90% of ζ-scores fell within acceptable limits. The overall reproducibility was about 22%, regardless of radon concentration levels, confirming the method’s robustness under real-field conditions. This retrospective study highlights the importance of ILCs in improving quality assurance for radon measurements and supports the development of standardized measurement protocols.