Radon and thoron progeny in Romanian Houses

The radiation dose from inhaled radon and thoron progeny indoors is the dominant component of population exposure to natural radiation sources accounting for about 60 per cent in Romania. The radon and thoron short-lived decay products concentrations have been measured in 670 typical urban and rural Romanian houses, randomly selected throughout the country. Our method used to determine the volumetric activity of 218 Po, 214 Pb, 214 Bi and 212 Pb is the active one of sucking a known volume of air (about 0.6 m3) through an open-faced high- efficiency filter paper (98%) at known flow rate (0.01-0.08 m3/min) for a certain collection time (usually 10 minutes) and counting the deposited activity with a ZnS alpha scintillation counter (40% efficiency) during four counting intervals, e.g. (1-4), (5-15), (16-30), (360-380) minutes. A computer program, very versatile in handling multiple input parameters, has been developed to solve the decay equations for obtaining the activity concentrations of daughters in air to calculate the Equilibrium Equivalent Concentrations (EEC) and the potential alpha energy concentrations. The detection limits of our method are, in optimum sampling and counting conditions, 1 Bq m-3 for each 218 Po, 214 Pb, 214 Bi and 0.1 Bq m-3 for 212 Pb. Internal exposure due to inhalation of radon and thoron progeny indoors and outdoors has been expressed in terms of effective dose. In dose estimates, the dose conversion coefficients adopted by the UNSCEAR- 2000 Report of 9 nSv/Bq h m-3 has been used for radon daughters and of 40 nSv/Bq h m-3 for thoron progeny, indoors as well as outdoors. An indoor occupancy factor of 0.75 and a population size of 22.68 mill. inhabitants (27% children and 73% adults) have been considered in all calculations. The population-weighted average of the EEC of radon and thoron indoors have been estimated at 24.9 Bq m-3 and 1.1 Bq m-3, respectively, with the corresponding average annual per capita effective dose of 1.88 mSv and 0.37 mSv, 2.25 mSv in total. Exposures for children have been calculated on the assumption that effective doses for the age group of up to ten years might on average by a factor of 2 higher than for adults. Outdoors values of EEC of 5.7 for radon and of 0.3 Bq m-3 for thoron and, consequently, of the correspondent annual per capita effective doses (0.09 mSv and 0.01 mSv), are much smaller. The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55112 man Sv. (authors)