Abstract
Radon has been identified as the second leading cause of lung cancer after tobacco smoking. 222Rn (radon gas) and 220Rn (thoron gas) are the most common isotopes of radon. In order to assess thoron contribution to indoor radon and thoron exposure, a survey of residential radon and thoron concentrations was initiated in 2012 with ∼4000 homes in the 33 census metropolitan areas of Canada. The survey confirmed that indoor radon and thoron concentrations are not correlated and that thoron concentrations cannot be predicted from widely available radon information. The results showed that thoron contribution to the radiation dose varied from 0.5 to 6 % geographically. The study indicated that, on average, thoron contributes ∼3 % of the radiation dose due to indoor radon and thoron exposure in Canada. Even though the estimated average thoron concentration of 9 Bq m−3 (population weighted) in Canada is low, the average radon concentration of 96 Bq m−3 (population weighted) is more than double the worldwide average indoor radon concentration. It is clear that continued efforts are needed to further reduce the exposure and effectively reduce the number of lung cancers caused by radon.
Highlights
Radon is a naturally occurring radioactive gas generated by the decay of uranium- and thorium-bearing minerals in rocks and soils
In order to assess thoron contribution to indoor radon and thoron exposure combined, a survey of residential radon and thoron concentrations was designed for homes in all 33 census metropolitan areas (CMAs) specified by Statistics Canada[14], which cover
During the summer of 2012, the research firm Prairie Research Associates (PRA) dialled over 100 000 telephone numbers in order to recruit at least 4000 participants from 33 metropolitan areas
Summary
Radon is a naturally occurring radioactive gas generated by the decay of uranium- and thorium-bearing minerals in rocks and soils. Because radon and thoron are members of different decay chains, their concentrations depend in part on the uranium and thorium levels in local soils and building materials. Because wood-frame construction is very popular for family houses, building materials contribute very little to indoor radon and thoron in Canada. Information on geographical distributions of uranium and thorium in the ground is limited or not available for many metropolitan areas of Canada, as shown in Figures 1 and 2 of a previous publication[3]. The previous study was able to demonstrate that average indoor radon and thoron concentrations in an area correlate well with the average uranium and thorium concentrations in the ground, even though the ratio of uranium and thorium concentrations could vary significantly from one area to another
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