Radon Daughter Exposures in the U.K.

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Abstract
Exposure due to the inhalation of the short-lived daughters of 222Rn is the single largest contributor to the exposure of the U.K. population. A survey of dwellings situated largely in the centres of population indicates an annual exposure of 0.16 WLM, on the average. On the basis of current knowledge this is equivalent to an annual effective dose equivalent of 800 μSv. This compares with the overall average of the effective dose equivalent from natural radiation of almost 1900 μSv in a year. The distribution of exposures to the short-lived daughters of 222Rn is markedly skew and indicates that some dwellings support concentrations of these daughters leading to exposures in excess of 1 WLM in a year. The areas of the U.K. in which exposures above this level are most likely to occur are regions with enhanced uranium mineralisation. These areas are sparsely populated and high exposures here do not significantly affect the overall average exposure of the population to radon daughters. An intensive survey of radon and radon daughters concentrations in one predominantly igneous region is reported. The average exposure for the 250 dwellings in this region surveyed so far was estimated to be 1.3 WLM in a year, a factor of 8 greater than the national value. About 5% of the homes exceed 5 WLM in a year. Measurements of equilibrium factor indicate that plate-out contributes to the removal of radon daughters from room air. In general, the equilibrium factor measured indicates an unattached fraction of 218Po of less than 10%.