Radon permeability and radon exhalation of building materials

High radon concentrations indoors usually depend on the possibilities of radon penetration from thesurrounding soil into the buildings. Radon concentrations in dwellings up to 100 kBq/m were found insome special regions (i.e. Schneeberg/Saxony, Umhausen/Tyrol) where the soil shows a high uraniumcontent and additionally a fast radon transport in the soil is possible. To reduce the radon exposure ofthe inhabitants in these "radon prone areas" it is necessary to look for building and insulating materialswith low radon permeability. We examined several building materials, like cements, concretes andbricks of different constitutions for their diffusion coefficients and their exhalation rates. Theinsulating materials, like foils and bitumen were tested also on their radon tightness.The measurements were performed with an online radon measuring device, using electrostaticdeposition of polonium-218 ions onto a surface barrier detector and subsequent alpha spectroscopy.The mean diffusion lenghts for the investigated building materials range from lower than 0.7 mm (i.e.For plastic foil) up to 1.1 m for gypsum. The diffusion length R was calculated from the diffusioncoefficient D with R??D??. If the thickness of the material is more than three times the diffusionlength, then it is called radon-tight. The mean radon-222 exhalation rates for the building materialsvaried between 0.4 mBq/m2s and 0.05 mBq/m2s.The samples were investigated as stones, plates, blocks, foils, coatings, powders etc., no statement canbe made about working up at the construction of a building. Also the fabrication and processing of thematerials has to be considered, because the material characteristics may changed.