Simultaneous measurements of radon and thoron, and their progeny levels in dwellings on anticlinal structures of Assam, India

Characteristics of 222Rn and 220Rn equilibrium factors in the indoor environments

Humans receive a significant portion (˃50%) of the total dose attributed to all the natural radiation sources from indoor radon (222Rn), thoron (220Rn), and their progeny. While progeny contributes an overwhelming part to the dose, in most surveys, only radon gas is measured because of the simplicity of measurement. Progeny concentration is usually estimated by multiplying gas concentration with an assumed factor, called the equilibrium factor, and taken from literature. Recently, results of the measurements of equilibrium factors for 222Rn and 220Rn were reported from various parts of the globe. In India, many such studies have been conducted in the current decade. The studies show a wide variation of equilibrium factors which suggests that they depend on environmental factors and measurement conditions. Therefore, they should be determined site specifically if accurate site-specific dose estimation is targeted. This paper summarizes concepts, definitions, and methods to determine equilibrium factors and reviews literature about reported equilibrium factors worldwide, focusing on data reported from India.

Radiological risk estimation from indoor radon, thoron, and their progeny concentrations using nuclear track detectors

In this paper, we report the results of seasonal variations of indoor radon and thoron concentrations, equilibrium factors for gas progeny, and radiological risks to dwellers in the hilly area of Guwahati City, Assam, India. Twin-cup dosemeters with LR-115 (II) nuclear track detectors were used in this study. The findings show that values vary significantly, with winter having the highest values and summer having the lowest, with spring and autumn having moderate values. In winter, radon concentrations range from 61.6 ± 11.2 Bq m^-3 (Mud) to 115.3 ± 34.3 Bq m^-3 (AT), with geometric mean values of 69.2 ± 13.8 Bq m^-3 and 109.4 ± 27.9 Bq m^-3, and in summer, they range from 21.1 ± 5.9 Bq m^-3 (Mud) to 28.4 ± 8.3 Bq m^-3 (AT), with geometric mean values of 22.7 ± 6.3 Bq m^-3 and 26.1 ± 7.1 Bq m^-3, whereas thoron concentrations range from 13.1 ± 5.1 Bq m^-3 (Mud) to 58.8 ± 12.6 Bq m^-3 (AT), with geometric mean values of 27.6 ± 7.0 Bq m^-3 and 52.9 ± 10.1 Bq m^-3 in winter, respectively, and in summer, from 8.8 ± 2.3 Bq m^-3 (Mud) to 13.0 ± 5.5 Bq m^-3 (Mud), with a geometric mean value of 1.87 ± 1.29 Bq m^-3. Radon and thoron progeny levels are reported to vary from 4.1 ± 0.3 mWL (Mud) to 15.1 ± 4.3 mWL (AT) and 2.6 ± 0.9 mWL (Mud) to 14.3 ± 4.2 mWL (AT) in winter and from 1.5 ± 0.7 mWL (AT) to 3.0 ± 2.5 mWL (Mud) and 0.9 ± 0.3 mWL (AT) to 2.7 ± 0.5 mWL (Mud) in summer, respectively. The equilibrium factors for radon and its progeny have been reported to range from 0.23 ± 0.1 (Mud) to 0.51 ± 0.3 (AT) in winter, whereas from 0.23 ± 0.1 (AT) to 0.48 ± 0.4 (Mud) in summer, respectively. The equilibrium factors for thoron and its progeny have been estimated in the range of 0.02 ± 0.01 (Mud) to 0.09 ± 0.06 (AT) in winter, whereas 0.02 ± 0.02 (AT) to 0.07 ± 0.05 (Mud) in summer, respectively. The inhalation dose rates differed from house to house, having values in the range of 1.2 ± 0.2 mSv year^-1 (Mud) to 4.6 ± 1.3 mSv year^-1 (AT) in winter, whereas 0.5 ± 0.3 mSv year^-1 (AT) to 0.9 ± 0.5 mSv year^-1 (Mud) in summer, respectively. The effective doses (EDs) due to the exposure of radon and thoron in the study area have been found to range from 2.5 ± 0.3 mSv (Mud) to 9.1 ± 2.7 mSv (AT) in winter and 0.9 ± 0.4 mSv (AT) to 1.8 ± 1.3 mSv (Mud) in summer, respectively. The levels of radon and thoron in similar types of construction were found to be significantly different from one house to another. The estimated radon and thoron concentrations in the houses of that region during winter are found to be substantially higher than the global averages as reported by UNSCEAR.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part I: 222Rn

Radon exposure limits are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, the equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 20 countries, measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of equilibrium factors suggests that location-specific values are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part II: 220Rn

Radon exposure levels are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 13 countries and regions measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here as the second of a two-part series, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of measured equilibrium factors suggests that location-specific values measured in the typical breathing zone are more appropriate than a worldwide average value in the calculation of lung bronchial dose.