Practical cut-off value for radon concentration in indoor air using an activated-charcoal radon collector

The World Health Organization (WHO) recommends that countries adopt the reference level of 100 Bq m-3 for indoor radon gas. Adopting the reference level requires a preliminary assessment of the indoor radon concentration. In the preliminary investigation, a cut-off value is useful, which is a value for selecting samples that can be reliably determined to be below the reference level (in this paper, the WHO reference level) using a straightforward method. If the true value was the WHO reference level, then the cut-off value of the PicoRad collector for selecting samples was determined as 80 Bq m-3 through the analysis of the 95% prediction interval.