Measurements of radon and thoron progeny concentrations in dwellings of Tehri Garhwal, India, using LR-115 deposition-based DTPS/DRPS technique

Indoor inhalation dose assessment for thoron-rich regions of Indian Himalayan belt

²²²Rn, ²²⁰Rn, and their decay products are significant contributors to background radiation dose. Their concentration level, pertaining exposure, and consequent dose are prime concerns in indoor environments. The present study was performed in 101 dwellings of different villages of Almora district situated in Kumaun hills of Indian Himalayan belt. Measurement of gases and decay products were made in three different types of dwellings (i.e., mud, cemented, and stone with plaster) in three seasons (winter, summer, and rainy). Concentration values for ²²²Rn and EERC were found to be varying in the order of winter > summer > rainy while obtained least in rainy season for the case of ²²⁰Rn and EETC. Concentration values for ²²²Rn and EERC were found to be lesser for cemented houses. Relative standard deviation of concentration values was found to be higher for the rainy season. Yearly averaged concentration values for ²²²Rn, EERC, ²²⁰Rn, and EETC were noted to be higher than the global averages but comparable to some Indian studies. Annual inhalation dose due to ²²²Rn, ²²⁰Rn, and their progeny was found to be 0.55-4.71 mSv/year with an average value of 2.36 ± 0.83 mSv/year. These values were measured for the first time in the study area and provide a link for future studies in the dwellings representing higher concentration values.

CONTRIBUTION OF THORON AND PROGENY TOWARDS INHALATION DOSE IN A THORIUM ABUNDANT BEACH ENVIRONMENT

In an environment having thorium rich soil the activity concentration of thoron in soil gas and ground-level outside air is comparable to that to radon. Recent reports indicate that in terms of the energy of the alpha particle decays of thoron's progeny, its concentration in indoor air is significant, typically about half that due to radon progeny. We made a detailed radiometric profiling of inhalation dose to the population of the high background radiation area in the west southern coastal region of India. Here we report the results obtained from the long-term time integrated passive measurements of radon, thoron and their progeny concentrations in the high background radiation areas of Chavara and Neendakara hamlets of Kollam district. The equilibrium factors of radon and thoron with their progeny were determined for the region and was consistent with a previous study. The estimated value of total annual inhalation dose in the region ranged from 0.4 ± 0.06 to 3.7 ± 0.6 mSv y-1. The annual effective dose due to thoron and thoron progeny contributes ~35% to the total inhalation dose which means that thoron and its progeny is significant in assessing the radiation dose to the public.

Seasonal variability of equilibrium factor and unattached fractions of radon and thoron in different regions of Punjab, India

A survey was conducted to estimate equilibrium factor and unattached fractions of radon and thoron in different regions of Punjab state, India. Pin hole based twin cup dosimeters and direct progeny sensor techniques have been utilized for estimation of concentration level of radon, thoron and their progenies. Equilibrium factor calculated from radon, thoron and their progenies concentration has been found to vary from 0.15 to 0.80 and 0.008 to 0.101 with an average value of 0.44 and 0.036 for radon and thoron respectively. Equilibrium factor for radon has found to be highest in winter season and lowest in summer season whereas for thoron highest value is observed in winter and rainy season and lowest in summer. Unattached fractions of radon and thoron have been found to vary from 0.022 to 0.205 and 0.013 to 0.212 with an average value of 0.099 and 0.071 respectively. Unattached fractions have found to be highest in winter season and lowest in rainy and summer season.

STUDY OF RADIATION EXPOSURE DUE TO RADON, THORON AND PROGENY IN THE INDOOR ENVIRONMENT OF YAMUNA AND TONS VALLEYS OF GARHWAL HIMALAYA

Long-term measurements of indoor radon, thoron and their progeny concentrations have been carried out in dwellings of Yamuna and Tons Valleys of Uttarkashi, Garhwal Himalaya to investigate the health risk associated with inhalation of radon, thoron and progeny. The experimentally determined values of radon, thoron and progeny concentrations were used to estimate the annual inhalation doses and annual effective doses. The annual inhalation dose has been found to vary from 0.8 to 3.9 mSv y^-1 with an average of 1.8 mSv y^-1 The annual effective dose from the exposure to radon and its progeny in the study area has been found to vary from 0.1 to 2.4 mSv with an average of 1.2±0.6 mSv. Similarly, the annual effective dose due to thoron and its progeny has been found to vary from 0.2 to 1.5 mSv with an average of 0.6±0.4. The measurement techniques and results obtained are discussed in detail.

Dose estimation derived from the exposure to radon, thoron and their progeny in the indoor environment

The annual exposure to indoor radon, thoron and their progeny imparts a major contribution to inhalation doses received by the public. In this study, we report results of time integrated passive measurements of indoor radon, thoron and their progeny concentrations that were carried out in Garhwal Himalaya with the aim of investigating significant health risk to the dwellers in the region. The measurements were performed using recently developed LR-115 detector based techniques. The experimentally determined values of radon, thoron and their progeny concentrations were used to estimate total annual inhalation dose and annual effective doses. The equilibrium factors for radon and thoron were also determined from the observed data. The estimated value of total annual inhalation dose was found to be 1.8 ± 0.7 mSv/y. The estimated values of the annual effective dose were found to be 1.2 ± 0.5 mSv/y and 0.5 ± 0.3 mSv/y, respectively. The estimated values of radiation doses suggest no important health risk due to exposure of radon, thoron and progeny in the study area. The contribution of indoor thoron and its progeny to total inhalation dose ranges between 13-52% with mean value of 30%. Thus thoron cannot be neglected when assessing radiation doses.