Natural radioactive substances
The earth’s crust contains radioactive substances with very long half-lives some of even more than 500 million years. Typical examples are uranium, thorium and potassium-40. Radiation from these substances reaches us via the soil and building materials. This natural radiation reaches us in two ways: as external radiation or internal contamination via food or inhalation, which we refer to as internal exposure
The radioactive noble gas, radon, occurs spontaneously from natural uranium. This gas moves freely through soil and building materials so that some of it ends up in the atmosphere. A large share of the natural radiation we receive originates from the inhalation of radon gas.
The natural radioactivity of the soil varies from location to location. In the south of Belgium, i.e. the Ardennes, Condroz and Sambre and Meuse region, the radon concentrations are much higher than in Flanders or the Netherlands. It is caused by high radon infiltration from the rocky ground.