Radon has been identified as the second leading cause of lung cancer after tobacco smoking. (222)Rn (radon gas) and (220)Rn (thoron gas) are the most common isotopes of radon. In this study, thoron exposure in Canada was assessed based on three community radon/thoron surveys conducted recently. It was confirmed that thoron was detectable in most homes and thoron progeny were present in every home surveyed. Results demonstrated that thoron concentrations varied more widely than radon. No clear correlation between (222)Rn and (220)Rn concentrations was observed in simultaneous measurements. It is estimated that thoron contributes to about 7 % of the radiation dose due to indoor radon exposure based on measurements in about 260 individual homes. Because indoor measurements and geological gamma-ray surveys did not support a reasonable association between (222)Rn and (220)Rn, thoron concentrations could not be predicted from widely available indoor radon information. In order to better assess thoron exposure in Canada and thoron risk to the Canadian population in various geographic locations, more thoron progeny measurements are required.

Vapour barrier membranes are often used as soil gas retarder in building construction. While vapour permeance characteristics of these membranes are well known and specified in Canadian standards, their radon diffusion coefficients are yet not available. This study provides test results of radon diffusion coefficients for 10 vapour barrier membranes commonly used in Canadian building construction.

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The Ministry of Sustainable Development, Environment and Parks of Québec (Ministère du Développement durable, de l'Environnement et des Parcs du Québec-MDDEP) held a 3-d provincial nuclear emergency response exercise in September 2008 that saw participation from Canadian provincial and federal departments. Nuclear emergency exercises are regularly held in Québec, given the presence of the Gentilly-2 nuclear power plant situated in Bécancour on the St. Lawrence River. The significance of this exercise is that it marks the first exercise held in Canada where environmental samples spiked with relevant radioisotopes were analyzed during the exercise, both on-site and remotely, and where the results of those analyses had a direct impact on the decisions made during the exercise. Following the exercise, samples were sent to two other laboratories that are part of the Canadian National Nuclear Laboratory Network for analysis, providing the first intercomparison exercise for the Network. The results of the analysis of the air and drinking water samples, as well as the lessons learned during the exercise, are presented and discussed in this article.