| Studies on environmental radon and its biological effects |
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Radon (222Rn and 220Rn) and its decay products are the most important contributors to human radiation exposure from natural sources. According to the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) 2000 report, the arithmetic mean concentration of indoor radon among countries is 46
Bq/m3. The average concentration in Japan is low, 16
Bq/m3. About half the natural radiation dose to humans is due to radon and its decay products. It is well known that exposure to high levels of radon causes lung cancer, but as yet there is little data on the effects of long-term exposure to low levels of environmental radon. The research activities of the Radon Research Group are directed toward understanding these effects. These activities include radiation measurement, aerosol physics, cell biology, genetics, health physics, and risk analysis.
It is expected that research activities will contribute to understanding the risk to humans of low-dose alpha exposure.
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Elements that are naturally radioactive include uranium, thorium, carbon, and potassium, as well as radon and radium.
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Uranium is the first element in a long series of decay that produces radium and radon. Uranium is referred to as the parent element, and radium and radon are called daughters. Radium and radon also form daughter elements as they decay.
The decay of each radioactive element occurs at a very specific rate. How fast an element decays is measured in terms of the element "half-life", or the amount of time for one half of a given amount of the element to decay. Uranium has a half-life of 4.4 billion years, so a 4.4-billion-year-old rock has only half of the uranium with which it started. The half-life of radon is only 3.8 days. If a jar was filled with radon, in 3.8 days only half of the radon would be left. But the newly made daughter products of radon would also be in the jar, including polonium, bismuth, and lead. Polunium is also radioactive - it is this element, which is produced by radon in the air and in people's lungs, that can hurt lung tissue and cause lung cancer.
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