Navigation and service

Ionising radiation

Environmental Radioactivity - Medicine - Occupational Radiation Protection - Nuclear Hazards Defence

Ionisierende Strahlung

What is radon?

Glossary Entryradon

Radon is a noble gas which is colourless, odourless and flavourless, does not bind and escapes via cracks and gaps from the earth into the breathing air. Radon exists only as radioactive isotopes. Radon-222 is the isotope with the longest half-life. It is a natural decay product of the uranium-thorium series which exists all over the earth and contributes considerably to the natural environmental radioactivity. Through further decay further radioactive decay products are generated which enter the lung via the breathing air and emit there, among others, alpha radiation. This can damage the cells of the lung. These damages can favour the generation of cancer.

The earth’s crust contains the natural radionuclides

  • Uranium-238,
  • Uranium-235,
  • Thorium-232, and
  • Potassium-40.

As intermediate product of the uranium-238 decay chain, the radioactive noble gas radon-222 (half-life 3.8 days) is produced from radium-226. It is colourless, odourless and flavourless.

Radon hardly undergoes chemical reactions with other elements and is therefore particularly mobile. Based on these properties, radon occurs everywhere in the world. From all materials containing uranium, especially from the soil and the building materials, radon is released into the free atmosphere or into the indoor air of buildings.

As an annual average, radon concentrations between 3 and 40 becquerel per cubic metre are normally measured in outdoor ground-level air in Germany (with a mean value of 9 becquerel per cubic metre). As a result of human interventions in nature, such as mining, changes may occur leading to a locally enhanced radon concentration above the natural level typical of that region.

Radon concentrations in dwellings

The mean value of radon concentrations in dwellings in Germany is about 50 becquerel per cubic metres; however, the radon concentration varies clearly from building to building. Annual mean values between ten and some thousand, in rare cases over 10,000 becquerel per cubic metre are measured. The most important reason for high radon concentrations in dwellings is radon from the building underground.

During the radioactive decay of radon other radioactive substances are produced. These are isotopes of the heavy metals polonium, bismuth, and lead. Especially the short-lived radon decay products deposit at the very fine particles in the air (aerosols) and thus remain floating over a long period of time. They can be inhaled together with the radon and thus lead to a radiation exposure of the lung tissue in particular.

There are different measuring methods to measure radon concentrations in dwellings.

Exposure to radon

According to recent findings, five to ten per cent of the lung cancer cases in the German population can be attributed to the exposure to radon and its decay products in buildings. Extensive investigations have shown that the lung cancer risk more than doubles with a radon concentration of 1,000 becquerel per cubic metre, compared with concentrations of below 50 becquerel per cubic metre.

As opposed to the occupational exposure to radon, there are currently no legal regulations in the private domain.

State of 2016.11.03

© Bundesamt für Strahlenschutz