Simultaneous 222Rn and 220Rn measurements in Winnipeg, Canada

Abstract

Naturally occurring isotopes of radon in indoor air are identified as the second leading cause of lung cancer after tobacco smoking. Winnipeg had the highest radon ((222)Rn) concentration among 18 Canadian cities surveyed in the past. There is great interest to know the current radon as well as thoron ((220)Rn) concentrations in Winnipeg homes. Therefore, radon-thoron discrimination detectors were deployed in 117 houses for a period of 3 months. The results confirmed that thoron is present at detectable levels in about half of the Winnipeg homes and radon remains significantly higher than the national average. In this study, radon concentrations ranged from 20 to 483 Bq m(-3) with a geometric mean of 112 Bq m(-3) and a geometric standard deviation of 2.07. It is estimated that 20% of Winnipeg homes could have radon concentrations above the Canadian indoor radon guideline of 200 Bq m(-3). This conclusion is similar to the previous estimation made 20 y ago. Thoron concentrations were below the detection limit in 60 homes. Among the homes with detectable thoron concentrations, the values varied from 5 to 297 Bq m(-3), the geometric mean and standard deviation were 21 Bq m(-3) and 2.53, respectively.

Long Term Measurements of Indoor Radon Equilibrium Factor

“…All detectors were analyzed by the National Institute of Radiological Sciences in Chiba, Japan. Detailed descriptions of RADUETs were given in previous publications (Tokonami et al 2005;Chen et al 2009). …”

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.…”