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This paper reports the measurements of indoor radon and thoron concentrations in selected Northern Indian dwellings (differing in ventilation rate). These were carried out using single entry pin hole based radon thoron dosimeters. In order to correlate the indoor levels with source term, the radon and thoron exhalation rates from soil samples collected from the same dwellings were also measured. Active measurement techniques with scintillation radon monitor and scintillation thoron monitor were used for exhalation measurements from soil sample. For thoron exhalation rate measurements, a small volume chamber was used. The indoor radon and thoron concentration in different rooms varied from 14 to 97 Bq/m3 and 23 to 189 Bq/m3, respectively. The radon mass exhalation and thoron mass emanation rates of soil samples varied from 28.2 to 91.2 mBq/kg/h and 3.42 to 12.1 mBq/kg/h, respectively. A weak correlation was found between indoor concentration and soil exhalation rates for these dwellings. Indoor radon concentrations from various rooms in the dwellings were lower than the limit (100 Bq/m3) recommended by WHO (2009).

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Ex ten sive work has been car ried out on mea sure ment of ra don and thoron lev els in in door envi ron ment in last three de cades. These stud ies are im por tant from ra di a tion pro tec tion point of view, if one con sid ered the con tri bu tion of ra don, thoron and their de cay prod ucts to to tal in ha la tion dose. Nu mer ous stud ies on ra don mea sure ment well es tab lished the be hav iour of its dis per sion in dwell ings. But the short lives of thoron cause the dif fi culty to un der stand the dis tri bu tion of thoron in dwell ings. The prob lem be comes more com pli cated when thoron dis per sion is stud ied un der dif fer ent in let air flow rate. Dif fer ent air flow pat tern may cause dif fer ent thoron level at dif fer ent point in test dwell ings caus ing un cer tainty in the mea surements. This work uti lized the CFD sim u la tion tech nique for study of in door thoron dis persion in test dwell ings un der nor mal and tur bu lent flow of air. The sim u la tion study for thoron dis tri bu tion in a test room was per formed for air ve loc i ties 0.10 ms-1 , 0.25 ms-1 , 0.50 ms-1 , 1.0 ms-1 , 1.5 ms-1 , and 2.0 ms-1. The re sults show that the thoron dis tri bu tion be comes uniform for the in let ve loc ity more than 0.5 ms-1 and ap pro pri ate to mea sure in door thoron concen tra tion. While in nor mal con di tion the mea sured thoron level var ies de pend ing upon the lo ca tion of do sim e ter. Thoron dif fu sion and mi gra tion length are also in creased with air flow rate.