Indoor Radon Measurements in Argentina

Rn is the most important source of natural radiation and is responsible for approximately half of the received dose of the totality of the sources. Most of this dose comes from the inhalation of the progeny of Rn, and this happens especially in closed atmospheres. Due to this, the control of the levels of Rn concentration in the different geographic areas is important where human activities are developed. The radon gas concentration has been measured in houses of different cities of the Argentine Republic. The chosen cities of the different provinces are representative of the different geologic zones from our territory: uraniferous zone, mountainous zone, level land and sedimentary zone. For this purpose, they were used as measurement methods nuclear track detectors, electret detectors and detectors based on activated charcoal adsorption. A total of 1994 houses were analyzed from 1983 to the date. The studied cases were houses in which the predominant materials of construction are concrete and brick. The average values found in the different cities do not exceed 50 Bq/m. The values over 200 Bq/m are very few and none of them overcome a value of 300 Bq/m. The average value of our country is 33.8 Bq/m, with a geometric mean of 23,9, being the effective annual dose of 0.84 mSv. For this reason, it can be assumed that, until this moment, the indoor radon levels in the Argentine Republic are within acceptable values for the population, not causing significant radiological risk. Introduction In the last few years national authorities and the public in general have shown a renewed interest in natural radiation and the environment and in particular in the concentration of radon gas in homes. In some countries, the concentration of radon gas in dwellings is now subject to legislation due to the high doses found as a consequence of the elevated radon concentrations measured. This is especially true in countries with cold climates where, due to the energy crisis of the seventies, homes were built more hermetically so as to minimise uncontrolled ventilation. Radon gas is the most important natural radiation source and the one that most contributes to the effective dose received by man from natural sources. It has been estimated that radon and its short lived decay progeny contribute with three quarters of the annual effective dose received by man from natural terrestrial sources and is responsible for about half of the dose from total sources (1). Radon emanates to a certain degree from all the different types of soils and its concentration in the atmosphere depends upon the uranium and radium concentrations present in the soils. Its presence in the biosphere is due to its semidesintegration period of nearly 4 days, which allows it to diffuse from the earth’s crust into the air we breath. The radiological importance of radon does not lie on the concentration of radon gas itself, but in that of its short lived decay daughters, polonium, bismuth and lead which are inhaled and deliver the bronchial radiation dose. The mean concentration levels of Rn in air over continents are in the range of 1-10 Bq m (1). The factors which influence the diffusion of radon from the soil into the air are (2): The uranium and radium concentration in soil and rocks. The emanation capacity of the ground. The porosity of the soil or rock. Barometric pressure gradient between the interfaces. Soil moisture and water saturation grade of the medium. Other variables. The mean emanation rate for continental soils is 16 mBq m s . The concentration of indoor radon depends on the emanation rate of the gas from the soil, of the content of the precursor nuclide Ra, and the ventilation rate of the dwelling. It is important to remember that although a reduced ventilation rate helps to increase the radon concentration and that of its daughters in air, it is predominantely the presence of an important emanation source such as a Ra rich soil or construction material the principal cause of a high radon concentration. Many different measurement techniques have been developed to determine the radon concentration in air, such as thermoluminicent detectors (3), solid state nuclear track detectors (4), electret detectors (5) and devices based on the absorption of radon gas by activated charcoal (6).