Fundamental research on the reduction of indoor radon concentration

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Indoor radon ( ^<222>Rn) concentrations were measured so as to understand the behavior of radon in wooden houses. The number of measured houses was 28 buildings which were located over a wide region from Hokkaido to Kagoshima. The measurement had been carried out for one to three years.The radon concentrations in wooden houses ranged from 3 to 22 Bq/m^3, and those in reinforced concrete houses were from 25 to 46 Bq/m^3 which were about 1.5 times as much as those in the wooden houses. In reinforced concrete buildings, the radon concentrations varied over a range of 21 to 1116 Bq/m^3. The large concentrations are due to radon emanation from many inorganic materials, and from the effect of small ventilation rates. In reinforced concrete buildings and under the floor of wooden houses, the radon concentrations were large from spring to summer. It was made clear that radon emanating from the soil under the floors enters the wooden houses. Therefore, the radon emanation could be reduced by covering the ground under the floors of the wooden houses with concrete or vinyl sheet.In the future, the wooden houses in Japan will become airtight one and the inorganic materials will be used much more, then the radon concentrations will be larger than nowadays like in the reinforced concrete buildings at this time.