- What are electromagnetic fields?
- Static and low-frequency fields
- What are static and low-frequency electric and magnetic fields?
- Direct and alternating voltage
- Effects of static and low-frequency fields
- Reports & Evaluations
- Radiation protection relating to the expansion of the national grid
- Basics transfer of electrical power
- High-frequency fields
- What are high-frequency fields?
- Applications high-frequency fields
- Radiation protection in mobile communication
- What is mobile communication?
- Reports and evaluations
- What is optical radiation?
- UV radiation
- What is UV radiation?
- Sun but safe!
- Effects of UV radiation
- Protection against UV radiation
- UV index
- Infrared radiation
- What is ionising radiation?
- Radioactivity in the environment
- Where does radioactivity occur in the environment?
- What is the level of natural radiation exposure in Germany?
- Air, soil and water
- Building materials
- Natural radionuclides in building materials
- Clay as building material
- Granite plates used in households
- Industrial residues (NORM)
- BfS laboratories
- Applications in medicine
- Radiation protection in medicine: international activities
- Applications in daily life and in technology
- Radioactive radiation sources in Germany
- Register high-level radioactive radiation sources
- Type approval procedure
- Cabin luggage security checks
- Radioactive materials in watches
- Ionisation smoke detectors (ISM)
- What are the effects of radiation?
- Effects of selected radioactive materials
- Consequences of a radiation accident
- Cancer and leukaemia
- Genetic radiation effects
- Individual radiosensitivity
- Epidemiology of radiation-induced diseases
- Ionising radiation: positive effects?
- Risk estimation and assessment
- Radiation protection
- Basic information
- Occupational radiation protection
- Nuclear accident management
- What is an emergency?
- What happens in an emergency?
- Federal and state tasks
- In the event of an emergency
- Measuring networks
- Exercises for emergency situations
- Defence against nuclear hazards
- Service offers
- Radon measurements
- Incorporation monitoring
- Biological dosimetry
- Online library
- About us
- Science and research
- Research concept
- Scientific collaborations
- EU research framework programme
- BfS research programme
- Third-party funded research
- Departmental research
- Selected research projects
- Selected research results
- Professional opinions
- Science Council
- Laws and regulations
- BfS Topics in the Bundestag
Clay as building material
- Common mineral house building materials such as concrete, brick, gypsum and aerated concrete contain natural radionuclides. This does usually not involve radiation exposure relevant to the house residents’ health.
- It is currently a matter of debate whether unfired clay building materials may result in radiation exposures critical to health, because unfired clay can emit the radioactive gas thoron into indoor air.
- Unlike radon of which both the occurrence in buildings and health effects have been studied well, thoron requires further research to facilitate a reliable evaluation of its health implications.
Common mineral house building materials such as concrete, brick, gypsum and aerated concrete contain natural radionuclides. This does usually not involve radiation exposure relevant to the house residents’ health.
It is currently a matter of debate whether unfired clay building materials may result in radiation exposures critical to health. The reason for this is because unfired clay can emit the radioactive gas thoron into indoor air. It cannot be ruled out that elevated thoron levels occur in indoor air in particular cases.
Radon-222 and Radon-220 (also termed thoron) both are isotopes of the natural gaseous element radon. The term "radon" usually signifies the isotope Radon-222 produced during the decay of uranium. The term "thoron" points to the fact that Radon-220 originates from the decay of thorium.
Unlike radon of which both the occurrence in buildings and health effects have been studied well, thoron requires further research to facilitate a reliable evaluation of its health implications.
Radon and thoron in buildings
A radon problem mainly occurs when a lot of radon from the subsoil enters a house. It has been established that elevated radon concentrations in buildings increase the lung cancer risk. Thoron is formed in the ground, too. However, with a half-live of only 55 seconds, it decays almost completely on its way from the ground into a house. Therefore, the subsoil is not a noteworthy source as to thoron – in contrast to radon – indoors. Elevated thoron levels can only occur when greater amounts of thorium from building materials are directly released into a house.
The assumption that unfired clay could give rise to health-relevant radiation exposure indoors is traced back to studies on traditional Chinese clay housings. Clay basically does not contain more uranium or thorium than other building materials, but it has a greater surface because it is very finely granulated. It is via that greater surface that more radon and thoron are released into indoor air than for instance with fired clay bricks. During stoving of bricks the grains fuse together, thereby reducing the surface. This is why fired clay bricks do not release relevant levels of radon and thoron.
The amount of radon and thoron actually occurring in clay correlates with its uranium and thorium level which varies considerably depending on its region of origin.
Further research required
Based on expansive scientific research it has been well established that radon in buildings can cause lung cancer. The risk of disease depends on the radon concentration.
As a general rule, thoron also has the potential to induce lung cancer. However, the concentration required to cause a marked increase in risk has been far less well established for thoron in indoor air than for radon. Only few studies have been carried out so far on the occurrence of thoron in buildings in Germany as compared to radon.
Further research is therefore necessary to facilitate reliable assessment of the health impacts of thoron in building materials in Germany.
Detection of thoron is difficult
For this reason, the Federal Office for Radiation Protection (BfS) has made important proposals to facilitate quality assured thoron measurements: Within the scope of departmental research the BfS has initiated and supervised the construction of calibration devices for thoron measurements at the Physikalisch-Technische Bundesanstalt (PTB, the National Metrology Institute of Germany) as well as a study of the Helmholtz-Zentrum Munich concerning the fitness of thoron measurement devices for national surveys.
BfS itself offers factory calibrations of thoron measurement instruments made in its accredited radon laboratory. Here, measuring instruments are exposed to exactly known thoron concentrations in order to ensure the accuracy of measurement results. This is a prerequisite for quality assured performance of thoron measurements which are technically very sophisticated.
State of 2018.03.28