Evaluation of radiation exposure from attached and unattached progeny fraction of radon and thoron in Kumaun Himalaya, India.

The present investigation was conducted to quantify the radiological exposure associated with inhalation of attached and unattached 222Rn and 220Rn progeny concentrations in indoor environments. The total progeny concentrations of 222Rn and 220Rn were estimated using direct progeny sensors, and the attached progeny concentrations of 222Rn and 220Rn were measured using wire-mesh-capped direct radon and thoron progeny sensors based on LR-115 type-II detectors. The obtained average unattached fraction of 222Rn progeny was 0.14, similar to the UNSCEAR recommended value, while the unattached fraction for 220Rn progeny was 0.09. In the different indoor conditions, the concentration of total progeny, attached and unattached progeny of 222Rn and 220Rn are higher in mud dwelling among mud, cement and stone dwellings. In addition to it, a seasonal variation was also studied, and a descriptive statistical analysis was done using a paired student's t-test to compare progeny fractions between dwelling types. Dose conversion factors for mouth and nasal breathing were further estimated separately and the average dose conversion factors for mouth and nasal breathing were found to be 19.5 ± 6.3 mSv/WLM and 8.5 ± 1.1 mSv/WLM, respectively. The annual effective dose is under the ICRP reference level, however, the inhalation dose estimated for mouth breathing was found to be more than twice that of nasal breathing. In the present study, the unattached radon progeny contributes 14.21 % to the annual effective dose (AEDR).