With the use of rocks and soils for construction purposes may result in these materials contained on or made them released radionuclides to the exposure of the population. Of particular importance are the radionuclides from the radioactive decay series of uranium-238 and thorium-232 and the potassium-40.
The cause is due to natural radionuclides in building materials caused by radiation exposure during their stay in buildings:
by the radionuclides in building materials emanating from outside the body to gamma radiation, acting
from the inhalation of the materials in the rooms released radon and its decay products.
Investigation and assessment
For more than 20 years in Germany conducted studies and assessments of radioactive substances in building materials. The Federal Office for Radiation Protection (BfS) are of more than 1500 samples of stone, building materials and mineral residues data for the specific activities of the relevant radionuclides. At a large number of samples was also determined that radon release.
The mean of the natural radionuclides in building materials by the related local gamma dose rate (ODL) in buildings is about 80 nano-Sievert per hour (nSv / h). Values of dose rate above 200 nSv / h are rare.
The radioactive decay of radium-226 is produced from radon-222 from the viewpoint of radiation protection is of particular interest. According to recent findings in Germany a few percent of the population of lung cancer from exposure to radon and its decay products are attributed to buildings.
Radon is of particular importance
The radon release from building materials is determined by the specific activity of radium-226 and others, determining the radon transport material properties (eg porosity) determined. Studies show that in Germany not in large quantities traditionally used building materials concrete, brick, aerated concrete and calcium-generally the cause of the overruns by the Federal Office for Radiation Protection recommended annual average value of radon concentration in living areas. This is 100 Bq / m³ not exceed (see Fact Sheet Natural radioactivity in building materials). The contribution of radon-222 is made of building materials for radon concentration in dwellings with a maximum of 70 Bq / m³. In current commercially available materials values well below 50 Bq/m3 were determined.
Higher radon concentrations at various construction materials
Rates of release of radon, the higher concentrations in the area may result, were in Germany isolated residues of combustion of coal with increased Uran-/Radiumkonzentration (formerly known as "coal slag" regionally used as a filling of ceilings), and in exceptional cases, natural stones measured with increased specific activities of radium-226. Elevated levels of radon in houses of Mansfeld copper slag, despite the relatively high specific activity of radium-226 is not determined in this material. In some countries, higher levels of radon have been found in houses, those found in so-called chemical gypsum (the residue Phosphoritverarbeitung) and also in lightweight concrete produced using alum. Occasionally there are also above-average radon concentrations in the traditional areas of mining, overburden or waste materials if the ore was used as a building material with enhanced radium concentration, as concrete or mortar and aggregate for foundations and backfill in house construction.
According to information currently used in Germany were no materials for building purposes, which could result from increased concentrations of thorium relevant from the viewpoint of radiation protection, exposure to radon-220 (thoron) and its decay products indoors.
Industrial residues as secondary raw material
In some residues from industrial processes to enrich the natural radioactive substances. When using these residues, such as their use as secondary raw materials in the construction industry are increased radiation exposure of the population can not be excluded. To avoid this, in Part A of Annex XII of the Radiation Protection Ordinance (Ordinance) called [1], the residues at the landfill or recycling aspects of radiation protection should be considered. The also in Appendix XII of the Radiation Protection Ordinance established control limits for the recycling of these materials is ensured that the applicable guideline for members of the public, the effective dose of 1 mSv per year is not exceeded.
According to the Construction Products Directive (89/106/EEC) [2] a construction may not be placed on the market in the Member States of the European Union if it meets the essential requirements of hygiene, health and environmental protection, among other things regarding the release of dangerous radiation, met . This policy is being implemented with the Construction Act [3].
Natural radionuclides in natural stones
Because today in all areas of construction inside the house and outdoor amplified natural stones are used, was investigated by the BFS, with the support of the German Natural Stone 'Association in 2006, a number of commercially available tiles and other sheet materials of different origins on the levels of natural radioactivity and radiation protection point of view evaluated.
The focus was on gamma-spectrometric measurements of the specific activities of radium-226, potassium-40 and thorium-232. The results are summarized in the graph. The median values shown (central values) mean, which is half of the samples tested above this level and 50% below.
The material breakdown is at this point to the rock. It must be pointed out that are used commercially for reasons which are geared to the specific applications, the processing and maintenance of materials, not always correct rock names. It must be for "granite" is not necessarily about granite, but this term is also used for gneisses, diorites, granodiorites and other rocks.
Specific activities of the examined natural stones
The specific activities of the examined natural stones are available for potassium-40 in the range between 10 Bq / kg and 1600 Bq / kg, for radium-226 from less than 10 Bq / kg and 355 Bq / kg and for thorium-232 from less than 10 Bq / kg and 330 Bq / kg.
For comparison and will complement the above table and from the Pavlidou et al. [4] published values noted.
The potential radiation exposure from the different materials depends not only on the concentration of radionuclides and radon release from the nature of their usage.
EU recommendation "Radiation Protection 112"
For their evaluation, there is no binding legal basis. However, in the EU Recommendation "Radiation Protection 112" [5] one has simply been recommended to-use method that allows on the basis of the determined specific activities of the above radionuclides and an exploratory assessment of specific modeling assumptions. If you're in this to the generally accepted value of the effective dose of 1 mSv / yr for members of the population from radionuclides of natural origin (except radon) is oriented to determine that the investigated current building materials - even in large-scale applications - even the tested natural stones in buildings are fully used.
[1] Verordnung über den Schutz vor Schäden durch ionisierende Strahlen (Strahlenschutzverordnung - StrlSchV) vom 20. Juli 2001 (BGBl. I S. 1714)
[2] Lutz, H.; Springborn, M.: Die Bauproduktenrichtlinie - Gegenüberstellung und Abweichungen, Ernst & Sohn, Verlag für technische Wissenschaften GmbH, Berlin
[3] Gesetz über das Inverkehrbringen von und den freien Warenverkehr mit Bauprodukten zur Umsetzung der Richtlinie 89/106 EWG des Rates vom 21. Dezember 1988 zur Angleichung der Rechts- und Verwaltungsvorschriften der Mitgliedsstaaten über Bauprodukte (Bauproduktengesetz - BauPG) vom 10. August 1992 (BGBl. I, S.149)
[4] Pavlidou, S.;Koroneos, A.; Papastefanou, C.; Christofides, G.; Stoulos, S.; Vavelides, M. : Natural Radioacvtivity of Granites Used as Building Materials in Greece. Bulletin of the Geological Society of Greece, Vol. XXXVI, 2004
[5] European Commission: Radiation Protection 112 „Radiological protection principles concerning the natural radioaactivity of building materials“, Luxembourg: Office for Official Publications of the European Communities, 2000, ISBN 92-828-8376-0
