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Ionising radiation

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

Ionisierende Strahlung


Radon is a natural radioactive noble gas that is odourless, tasteless and colourless. Radon is formed wherever its mother nuclide radium is present, for example in soil and in building materials. Radon is released into the open air and also into buildings from the subsoil. Elevated radon concentrations in indoor air may lead to health burdens. Besides smoking, inhaling radon is among the greatest risks for developing lung cancer. Small measures are often enough to significantly reduce radon levels and thereby the risk of disease.

radon, soil air, transport

What is radon?

Apart from the radionuclides of minor importance to radiation exposure to man, the earth’s crust contains the natural radionuclides uranium-238, uranium-235, thorium-232, and potassium-40. The radioactive noble gas radon-222 (half-life 3.8 days) is produced as intermediate product of the uranium-238 decay chain from radium-226. It is colourless, odourless and flavourless. In Germany, radon makes the largest contribution to the radiation exposure to the population due to natural radiation sources.

Radon in the soil

The radon arising in the soil partly reaches the surface and is released into the atmosphere. The exhalation rate strongly depends on the permeability of the soil and weather conditions (temperature, humidity, air pressure). Radon can also be dissolved in ground water and migrates in bedrock.

Via the respiratory tract radon and its decay products reach the lung

Health effects of indoor radon

Radon can accumulate in the ambient air of closed rooms. Particularly harmful are its short-lived progeny which can deposit in the respiratory tract. Alpha radiation that accrues during decay can promote lung cancer. According to statistical risk calculations, nearly 1,900 deaths yearly are due to indoor radon in Germany. Within the European Union, 20,000 deaths yearly can be attributed to indoor radon.

Paragraphenzeichen vor einer Mauer

Legal regulations for the protection against radon

Protection against radon is regulated in the Radiation Protection Act. The Act provides for various measures to protect human health in areas with high occurrence of radon. The measures affect both residential buildings and workplaces.

Radon Concentration in Germany

Radon map

The radon map of Germany provides orientation as to the regional distribution of the radon concentration in the soil air one meter below the surface. The calculation is besed on altogether 2,346 geologically representative measuring points and the geological map of Germany on a scale of 1:1,000,000. From this map it can be derived in which region and to what extent enhanced radon concentrations in buildings can be expected.

Radon in buildings

From the subsoil, radon reaches outside air and enters dwellings. The radon levels indoors depend on the formation of radon within the ground, the materials on the site, their properties relevant for radon transport, and the construction method. The annual mean value of radon concentrations indoors averages 50 Becquerel per cubic meter (Bq/m³).

Radon protection

Measures to provide protection against radon

It is reasonable to refurbish buildings with a radon exposure above an annual mean value of 100 becquerel per cubic metre compartment air. Such values are mainly measured in regions with high natural radon concentration in the soil. Persons staying in rooms with enhanced radon contents in the air over years, have a higher risk of contracting lung cancer. It is often sufficient to take small measures to reduce the radon concentration.

© Bundesamt für Strahlenschutz