Natural radiation exposure in UK dwellings

A survey of gamma-ray dose rates and radon concentrations in 2000 UK dwellings has been carried out. This shows the mean annual effective dose equivalents from gamma-rays and radon decay products in dwellings are 280 and 1000 μSv, respectively. When account is taken of exposures elsewhere, mean annual doses from these sources are about 350 and 1200 μSv, respectively, the latter being greater than previous estimates because of a reassessment of conversion factors between exposure and dose. Mean annual dose from thoron decay products is about 150 μSv. More detailed surveys in regions of the UK with elevated concentrations of natural radioactivity in rocks and soil have shown that radon concentrations vary widely, sometimes resulting in annual effective dose equivalents exceeding 100 mSv. Doses from gamma-rays and thoron decay products are much less variable, with maxima around 1 mSv/year. Although the radon concentrations indoors are clearly related to local geology, weaker influences can be discerned, such as the storey on which measurement is made and the presence of double glazing. (author)