Preliminary assessment of thoron exposure in Canada

Abstract

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.

The Concept of Equivalent Radon Concentration for Practical Consideration of Indoor Exposure to Thoron

“…There are various types of ATDs available commercially, some sensitive to thoron and some to radon only [12]. There are a few ATDs capable of measuring radon and thoron separately, such as the RADUET used in the simultaneous radon and thoron surveys in Canada [7,8,9,10]. …”

“…A total of 370 Canadian homes have been tested for thoron in addition to radon [7,8,9,10] with thoron detected in about half of those. Among the homes with detectable thoron concentrations, the values varied from 6 to 1977 Bq·m −3 with a population weighted average of 56 Bq·m −3 .…”

“…Research on thoron and its contribution to the total radiation exposure from radon isotopes (both radon-222 and radon-220) has been carried out since the beginning of the National Radon Program in 2007. Results of several small scale Canadian thoron surveys have been published [7,8,9,10]. It is estimated that thoron contributes about 8% of the radiation dose attributed to indoor exposure to both radon-222 and radon-220 in Canada.…”

“…However, the variation is large for various geographical locations and there are situations where exposure to thoron is much more significant. Simultaneous radon and thoron measurements were conducted in a total of 370 Canadian homes in five cities/communities [7,8,9,10]; the ratios between thoron and radon concentrations in individual homes varied widely with an average ratio of 0.67. Three point eight percent (3.8%) of homes had thoron concentrations more than five times the radon concentration.…”

Radon and Thoron (222Rn and 220Rn) Concentration Distribution Study on Three Detection Planes inside of a Closed Room Using Nuclear Track Methodology

“…A fact is that about half of the natural radiation exposure encountered by the population is due to inhalation of short-lived decay products of the naturally occurring radon ( 222 Rn and 220 Rn), and needs to be evaluated, in order to minimize the risk to the population [1][2][3][4][5][6][7][8][9][10]. The role of radon in the growth of lung cancer incidence, and other public health diseases has been proved and therefore the investigation requires particular attention on the concentration distribution in each position, inside of a room volume [11,12].…”