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In the framework of the EMPIR research project Metrology for Radon, a facility was devised that provides stable and traceable atmospheres for the realization of radon activity concentration at a high metrological level. The facility is used to calibrate and test devices for measuring radon in the air. It enables precise long-term exposures in the range between 100 Bq/m
Beck et al. (Wed,) studied this question.