Is there any health danger by radioactivity on the use of dimensional stones?

Abstract

Abstract

Natural building stones must be analysed according to a legally defined procedure to prove that the natural radioactivity they emit is below the so-called activity index given by European Commission. This applies in particular to rooms inside buildings or apartments that are used by people for longer periods of time. Gamma spectrometric measurements were determined for all nuclides involved, 40 K, 226 Ra and 232 Th, which were finally summed up to a total dose for each sample. Measurements are prescribed to check whether the reference value of 1 milli-Sievert per year can be exceeded by radionuclides in the respective building materials. Natural stones, 82 in total from all over the world, such as various igneous, metamorphic and sedimentary rocks, which are currently used as building stones for interior and exterior finishing, as kitchen worktops, floor tiles, wall cladding, table tops, furniture cover plates, paving stones, terrace slabs, paving slabs, stairs, street furniture, etc., were selected. Additionally, Rn-222 and Rn-220 exhaled per unit mass were determined simultaneously on 54 selcted from the total 82 rocks by using the accumulation method. In addition, our results were statistically compared with literature data, according to which fesic igneous rocks, gneisses and clay mineral-rich rocks have the highest potential to be radiologically threatening. Limestones, marbles, quartzites, mafic igneous rocks and sandstones are generally less radiologically harmful, but even here there are exceptions depending on the geological formation history and mineralogical composition. The highest activity index of 1.87 was determined for the gneiss Giallo California. Model calculations to determine the expected radiation exposure for a human were used by applying two less complex approaches. Even with the extreme model “coffin”, which consists of the Gialo California, a human experiences only a maximum dose rate of 1.29 mSva −1 , which is far below the maximum dose rate of 20 mSv a −1 allowed for occupational radiation exposure. The 220 Rn and 222 Rn are often neglected; however, their contribution to the dose rate received by the population may be significant. Model simulations for a room with 4 m × 3 m × 2.5 m where the walls and the floor coverd with tiles of 1 cm thickness show a maximum indoor radon concentration of less then 100 Bg m −3 . With increase in thickness of the tiles up to 3 cm, 10 cm and 20 cm and for poorly ventilated rooms especially some granitoids, gneisses and the copper-rich shale are above the allowed limit of the European Commission.