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.

Indoor radon and thoron concentration plays a vital role in the total effective dose in the indoor environments. In the present study, the measurement of indoor radon, soil gas radon concentration and the drinking water radon concentration was carried out in Rajpur area of Dehradun valley located near by the geological fault line named Main Boundary Thrust (MBT). The measurement was carried out using RAD-7, a solid state detector with its special accessory. The indoor radon concentration varies from 35 to 150 Bqm À3 with an average value of 85 Bqm À3. The soil-gas radon concentration varies from 2 to 12.3 kBqm À3 with an average value of 6.5 kBqm À3. Radon concentration in water samples varies from 1.7 to 57.7 kBqm À3 with an average value of 20 kBqm À3. These results are helpful for estimation of annual effective dose, ingestion dose and inhalation doses. The annual effective dose varies from 0.88 to 3.78 mSvy À1 with an average value of 2.13 mSvy À1. The annual ingestion dose due to drinking water was found to vary from 0.36 to 7.91 mSvy À1 with an average value of 3.92 mSvy À1. The annual inhalation dose was found to vary from 0.0042 to 0.1454 mSvy À1 with an average of 0.0504 mSvy À1 .

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In the present study, the measurements of indoor radon, thoron and their progeny concentrations have been carried out in the Rajpur region of Uttarakhand, Himalaya, India by using LR-115 solid-state nuclear track detector-based time-integrated techniques. The gas concentrations have been measured by single-entry pin-hole dosemeter technique, while for the progeny concentrations, deposition-based Direct Thoron and Radon Progeny Sensor technique has been used. The radiation doses due to the inhalation of radon, thoron and progeny have also been determined by using obtained concentrations of radon, thoron and their progeny in the study area. The average radon concentration varies from 75 to 123 Bq m with an overall average of 89 Bq m The average thoron concentration varies from 29 to 55 Bq m with an overall average of 38 Bq m The total annual effective dose received due to radon, thoron and their progeny varies from 2.4 to 4.1 mSv y with an average of 2.9 mSv y While the average equilibrium factor for radon and its progeny was found to be 0.39, for thoron and its progeny, it was 0.06.