Assessment of natural radiation levels due to ²²²Rn, ²²⁰Rn and progeny in indoor environment of outer Himalayan region, India

The study of measuring natural radiation levels resulting from natural radioactivity due to the concentration of radon (²²²Rn), thoron (²²⁰Rn) and progeny is important as they are the significant contributor to background radiation dose to inhabitants. The time integrated passive measurements were carried out in indoor environment of dwellings in the Champawat District of outer Kumaun Himalayan belt, Uttarakhand, India with the aim of investigating significant health risk to the inhabitants in the study area. The measurements were performed using single entry pinhole dosimeters and progeny sensors (DTPS/ DRPS) with the recently developed LR-115 detector-based solid state nuclear track detectors to measure indoor levels of ²²²Rn, ²²⁰Rn and their progeny concentrations, respectively. Further, the corresponding indoor gamma level was also measured in respective dwellings to assess indoor gamma dose rate. The estimated value of annual indoor ²²²Rn concentration lies in the ranges from 13.40 to 210.62 Bq/m³ whereas thoron concentration ranges from 19.72 to 179.0 Bq/m³ with the annual average of 85.0± 43.07 Bq/ m³ and 84.46 ± 36.89 Bq/m³ respectively. The observed value of gamma dose rate in indoors vary from 0.08 μSv/h to 0.32 μSv/h with an average of 0.18 ± 0.06 μSv/h. The annual average value of indoor radon was found to be greater than both the worldwide (40 Bq/m³) and national (42 Bq/m³) averages, but indoor radon concentration falls within reference limit of 200-300 Bq/m³ and in the same way, the annual average value of indoor thoron was found to be much higher than the worldwide and national averages of 10 Bq/m³ and 12.2 Bq/m³, respectively. The obtained results strengthen the current database as no study has been performed earlier in the present study area and the results so obtained are consistent with recent research done in the Indian Himalayan areas. (author)