Development of wood materials as a radon sealant

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Concrete and other inorganic construction materials emanate radon, which has radio-activity and stays in the air tightened room. It is said that people is affected by radioactivity and has a risk of lung cancer when they live in the room of a high radon concentrations for long time.The aim of this research is to seal the radon emanation from inorganic materials by using wooden materials as a radon sealant. It is expected that wooden materials reduce the radioactivity of radon during diffusing through wooden materials, because of its short half decay time of 40 minutes.Two methods were employed to evaluate the performance of radon sealant of wooden materials. A contract method ; As a sample block, an inorganic material board with high radon emanation were sandwiched with two wooden boards, surface to surface, and the edge was sealed with a glue. Radon concentration in a desiccator setting the sample block was monitored with a cup method. A non-contract method ; Radon concentrations was measured in the chambers separated by a sample board. Radon source was put in the one side of the chambers.As the results,1. Radon concentrations was reduced with the increases in the thickness of the sample. The order of the reduction rate from the highest reduction was soft wood plywood, lauan plywood, particle board and MDF.2. The reduction rate of MDF with 2.8mm thickness was 17% but the acrylic coating rose the reduction rate to 89%. 3. The wooden materials gave 7-30x10^<-5> cm^2/s as the diffusion coefficient of radon. 4. Charcoal reduces the radon emanation from the gypsum powder. The radon emanation of gypsum mixed with 15% of activated charcoal was reduced to 90%, and that of the mixture with charcoal of fir fiber was 70%.This study gave a possibility to develop a new interior materials which has high performance of radon sealant. Now we are evaluating the performance of the new gypsum board which was manufactured basing on this research.