Abstract
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.
Highlights
Since the inhalation doses are predominantly due to progeny of radon and thoron, and not due to the gases, it is important to measure the progeny directly
Out of 122 houses, radon concentration has been found ≤50 Bq/m3 in 89 houses, thoron concentration has been found ≤30 Bq/m3 in the 78 houses, equivalent radon concentration (EERC) has been found to be in the range 11 Bq/m3–30 Bq/m3 in 55 houses and equivalent thoron concentration (EETC) has been found ≤1 Bq/m3 in 55 houses
The annual average value of equilibrium factor for radon and its progeny has been found to be in good agreement with its globally assumed value (0.4) as reported in UNSCEAR28 and recently calculated value (0.42) for Garhwal Himalaya[37]
Summary
Since the inhalation doses are predominantly due to progeny of radon and thoron, and not due to the gases, it is important to measure the progeny directly. The progeny of radon and thoron have high diffusivities and ability to stick on the surfaces Due to this aspect, the freshly formed progeny quickly attach to existing aerosol particles, thereby giving rise to a consecutive activity size distribution. The freshly formed progeny quickly attach to existing aerosol particles, thereby giving rise to a consecutive activity size distribution This distribution is broadly classified into two groups, namely, the fine/unattached fraction (~2 nm diameter) and the coarse/attached fraction (~150 nm)[14]. The measurements of radon, thoron and their progeny concentrations were performed in 122 houses of Yamuna, Tons and Kedar valleys of Garhwal Himalaya. The attached and unattached progeny concentrations of radon and thoron were measured separately. The radiation doses (total annual inhalation dose and annual effective doses) were estimated from the measured values of activity concentrations
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