In the present study, indoor radon and thoron concentrations were assessed using a newly developed pin hole-based twin cup dosimeter with a single-entry face in some areas of Punjab state, India. The equilibrium equivalent concentrations of radon and thoron were estimated directly by using the newly developed progeny (decay products) sensors designed by Bhabha Atomic Research Centre, Mumbai, India. The average radon and thoron concentrations in the study region were found to be 61.6 ± 18.6 Bq/m3 and 68.0 ± 30.8 Bq/m3, respectively, while the average equilibrium equivalent concentrations of radon and thoron were 25.9 ± 7.7 Bq/m3 and 2.2 ± 0.7 Bq/m3, respectively. Calculated average equilibrium factor for radon and thoron was 0.45 and 0.04, respectively, in the present study. The annual inhalation dose that was calculated from the present observed concentrations varied from 1.1 to 4.1 mSv/year with an average value of 2.4 mSv/year, which is well within the reference level of 10mSv/year recommended by International Commission on Radiological Protection. The study shows that thoron is a significant contributor to the inhalation dose, which is about 29% of the total inhalation dose.
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