Uncertainties in Assessment of Indoor Radon Exposure. Terje Strand, Professor ScD, Norwegian Radiation Protection Authority and Dept. of Physics, University of Oslo, P.O.Box 55, N-1345 Oesteraas, Norway, telephone +47 67 16 25, fax +47 67 14 74 07, e-mail Terje.Strand@nrpa.no
Radon is the main source of exposure to ionising radiation of the Norwegian population. Large-scale surveys in Norway show that the average radon concentration in dwellings is between 50 and 100 Bq/m3, and that between 5 and 10% of the housing stock has an annual average radon concentration above the national action level of 200 Bq/m3. These estimates are mainly based on time-integrated measurements of the radon concentration using etched track detectors. However, these type of measurements are only surrogates of the exposure owing to the fact that most of the dose is due to deposition of short-lived radon daughters in the respiratory tract and that only a very small contribution is from the radon gas itself. Earlier studies show that the radon concentration is more closely related to the broncial dose than the concentration of the short-lived radon daughters, expressed in terms of equilibrium equivalent radon concentration (EEC), but this is not necessarily valid in indoor environments where the aerosol concentration is very high or very low, and/or the particle size distribution is very different from normal. In addition there are uncertainties in the assessment of average radon concentration owing to short-term (days/weeks) and long-term (months/years) variations in the radon concentration, placing of the detectors, ventilation habits during indoor occupancy, etc. This paper focuses on uncertainties in the assessment of radon exposure and health risk and data from Norwegian surveys will be used in the discussion.
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