Abstract
From 2007 to 2013, simultaneous radon (222Rn) and thoron (220Rn) measurements were conducted in a total of 3534 residential homes in 34 metropolitan areas covering 71% of the Canadian population. While radon levels were above the detector’s detection limit in almost all homes, thoron concentrations were measurable in only 1738 homes. When analysis was limited to homes where thoron concentrations exceeded the detection limit, a pooled analysis confirmed that thoron is log-normally distributed in the indoor environment, and the distribution was characterized by a population-weighted geometric mean of 13 Bq/m3 and a geometric standard deviation of 1.89. Thoron contribution to indoor radon dose varied widely, ranging from 1.3 to 32% geographically. This study indicated that on average, thoron contributes 4% of the radiation dose due to total indoor radon exposure (222Rn and 220Rn) in Canada.
Highlights
Radon is a naturally occurring radioactive gas generated by the decay of uranium- and thorium-bearing minerals in rocks and soils
While radon levels were above the detection limits (DLs) (3 Bq/m3) in almost all homes, thoron concentrations were below the DL
The highest radon concentration of 2341 Bq/m3 was measured in Halifax area, and the highest thoron concentration of 1977 Bq/m3 was found in the city of Fredericton
Summary
Radon is a naturally occurring radioactive gas generated by the decay of uranium- and thorium-bearing minerals in rocks and soils. Both uranium and thorium are found as trace elements in most rocks and soil in varying concentrations across Canada, as shown on the radioactivity map of Canada (Geological Survey of Canada 2014). Following the revision of the Canadian radon guideline from 800 to 200 Bq/m3 in June 2007, a number of regional and national radon and thoron surveys were conducted. This study summarizes data from simultaneous radon and thoron surveys conducted in a number of communities between
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