The annual effective dose from natural sources of ionising radiation in Canada

A review and analysis of published information combined with the results of recent gamma ray surveys were used to determine the annual effective dose to Canadians from natural sources of radiation. The dose due to external radiation was determined from ground gamma ray surveys carried out in the cities of Toronto, Ottawa, Montreal and Winnipeg and was calculated to be 219 muSv. A compilation of airborne gamma ray data from Canada and the United States shows that there are large variations in external radiation with the highest annual outdoor level of 1424 muSv being found in northern Canada. The annual effective inhalation dose of 926 muSv from Rn-222 and Rn-220 was calculated from approximately 14,000 measurements across Canada. This value includes a contribution of 128 muSv from Rn-222 in the outdoor air together with 6 muSv from long-lived uranium and thorium series radionuclides in dust particles. Based on published information, the annual effective dose due to internal radioactivity is 306 muSv. A program developed by the Federal Aviation Administration was used to calculate a population-weighted annual effective dose from cosmic radiation of 318 muSv. The total population-weighted average annual effective dose to Canadians from all sources of natural background radiation was calculated to be 1769 muSv but varies significantly from city to city, largely due to differences in the inhalation dose from Rn-222.