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Radon originating from radioactive decay of uranium and radium, which are naturally present in the Earth’s crust, is a common component of soil gas. The typical concentration of radon in the soil gas in the Czech  Republic is between 10 000 and 100 000 Bq/m³ (Becquerel per meter cubed) (Fig. 1). Soil gas with radon is released from the soil surface into the ambient air, where, due to dilution, radon occurs in concentrations ranging from 2 to 10 Bq/m³ (Fig. 2). The radon concentration in dwellings may be from 50 Bq/m³ upwards. There are houses where the concentration is at a level of thousands or tens of thousands of Bq/m³. The particular concentration is closely influenced by the amount of radon coming from the subsoil into the house (by the air tightness of the substructure of the house relative to the subsoil) and by the intensity of ventilation. If a high radon concentration is found in a house, relatively cheap and simple measures can be applied to bring the radon values down to an acceptable level. According to Czech legislation, the radon concentration in all habitable rooms in new dwellings must be lower than 200 Bq/m³, and in existing buildings it should be brought below 400 Bq/m³. Radon in the home is responsible for most of the irradiation that people are exposed to. This fact is documented by Fig. 4, which presents a pie graph with the distribution of irradiation from different sources.

Fig. 1 - Map of soil gas radon concentrations at the depth od 80 cm below the ground surface

Fig. 2 - Typical radon concentrations in the soil air, outdoor air and indoors.

Fig. 3 - Map of indoor radon concentrations on the territory of the Czech Republic.

Fig. 4 - Irradiation of humans from different sources