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Ionising radiation

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

Ionisierende Strahlung

Granite plates used in households

  • Natural stone and other building materials contain the natural radionuclides uranium-238, thorium-232 and their decay products as well as potassium-40.
  • As an intermediate of the uranium-238 decay chain, the radioactive noble gas radon-222 (Rn-222, half life 3.8 days) originates from radium-226.
  • However, in most instances the proportion of radon from building materials and natural stone in homes is small compared to the amount of radon emitted from soil.
  • If you are interested in granite for your home and would like to take account of radiation exposure, please ask the distributor or manufacturer for information on the radionuclide concentrations.

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.

In the past, newspapers reported about granite in homes as a source of potential radiation exposure. Natural stone and other building materials contain the natural radionuclides uranium-238, thorium-232 and their decay products as well as potassium-40.

As an intermediate of the uranium-238 decay chain, the radioactive noble gas radon-222 (Rn-222, half life 3.8 days) originates from radium-226. However, in most instances the proportion of radon from building materials and natural stone in homes is small compared to the amount of radon emitted from soil.

Granite countertops in homes

Granite is the name of stones that have solidified underground in greater depth from fluid magma. Granites frequently show enhanced concentrations of the nuclides from the uranium and thorium series and of potassium-40, compared to other building materials. Although mainly consisting of quartz, feldspar and dark, ferrous or magnesian minerals, their composition may vary broadly, depending on their geology and origin, which is recognisable by different colour and structure.

However, the correct name of stone is not always used in trade, based on considerations geared to the specific utilisations, processing and maintenance of materials. Thus, "granite" need not necessarily signify granite stone but this term is also used for gneiss, diorite, granodiorite, and other stones.

Radon: Cause of lung cancer

Radon is part of the natural decay chain of uranium-238 and is known to cause lung cancer. About 10 percent of lung cancers in Germany are related to radon, corresponding to about 2000 cases per year. The risk to contract lung cancer on account of radon in indoor air depends on the long-time indoor concentration.

However, comprehensive studies in Germany have clearly shown that enhanced indoor concentrations in the predominant number of cases are not due to radon escaping from building materials but to radon entering the house from the soil via the cellar. There are only very rare cases where enhanced indoor concentrations are being caused by the building materials used. This has been confirmed by recent studies on the radon release from building materials and natural stone (also including granite) conducted by the BfS during the last few years.

How ist the radionuclide content assessed?

There is currently no binding legal basis for the assessment of the radionuclide content of building materials. However, in its publication „Radiation Protection 112“, the European Union (EU) recommends an easy-to-use method which gives orientation for an evaluation which is based on the determined specific activities of the relevant radionuclides and on special model assumptions.

According to this publication, the granites investigated by the BfS can be used without restriction, even if they are used for large surfaces in buildings. The BfS does not have any information as to the utilisation of granites with particularly high radionuclide contents in living areas in Germany.

Recommendations

If you are interested in granite for your home and would like to take account of radiation exposure, please ask the distributor or manufacturer for information on the radionuclide concentrations. These are mostly known to the manufacturers, either in consequence of licensing procedures and import directives of third countries, or because they want to stand out from competitors.

Arrange for measurements of the radon concentration in your home. An increased radon concentration in homes represents a health risk to the inhabitants, independent of its origin. Laboratories for measurements, which are subjected to quality assurance in Germany, are participating in the annual comparative measurements for passive radon detectors of the BfS.

State of 2017.09.29

© Bundesamt für Strahlenschutz