Recent Research Subjects:
Elaboration of Estimation Methods of Atmospheric Transport Phenomena by Using Radon Isotopes and Their Decay Products
“Radon” (222Rn) and “thoron” (220Rn) are naturally occurring radioactive inert gases, which are exhaled from soil and building materials and then come into the atmosphere. Because of their simple generation and removal processes in comparison with other airborne materials, they are advantageous to analyze atmospheric transport by using them as tracers. Especially, radon has a half-life of 3.8 days that makes it a good representative of atmospheric transport with a scale of thousands kilometers, since, after travel around the earth by global atmospheric circulation, atmospheric radon has almost decayed out and disappeared. By using spacial and temporal variation in atmospheric radon concentration, we have elaborated our methods of estimation of atmospheric transport phenomena.
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Quantitative Clarification on Wet Deposition Processes by Using Radon and Its Decay Products
Airborne substances are transported by “wind,” and then efficiently deposited on the ground by “rain,” where most of people live. Rain
also flush and remove substances on the ground surface elsewhere. The decay products of radon and thoron, in contrast to their parents, are removed from the atmosphere due to rain. This removal process has similarities with precipitation-related removal processes of other contaminants in air. Analysis of radon decay products in air and rain results in further understanding of “wet deposition” processes.
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Analysis and Estimation of Release and Atmospheric Transport of Radioactive Materials Discharged by the Fukushima Dai-ichi NPP Accident
Whats were happened during the Fukushima Dai-ichi nuclear power plant accident in March 2011, and when did each event occur? How do they affect surrounding environment? Their elucidation must bring us fundamentals of a number of our lessons for future improvements and safety. Based on results of various environmental monitoring activities after the accident, we are applying knowledge and results of our study to clarify and understand processes of atmospheric dispersion and deposition of radioactive materials released into the atmosphere during the accident.。
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Environmental Safety Research Based on the Results of the Fukushima Dai-ichi NPP Accident:
Development of Rapid and Sophisticated Application of Environmental Monitoring Data to Analyze Radioactive Release
During the Fukushima Dai-ichi NPP accident in March 2011, partially caused by extensive damage to regional power supply and traffic due to the big earthquake and subsequent huge tsunami, insufficient observations of local meteorology and environmental radiation and radioactivity had been obtained with monitoring activities. What could we do for more effective monitoring at that time? Study on the emergency response and countermeasures against the situation at that time is needed for our understandings and solutions to the lessons from the accident.
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Evaluation of Behavior of Indoor Radioactive Aerosol Caused by Radon Decay Products
In tightly enclosed artificial environments such as indoor or underground spaces, high radon and thoron concentrations in air occur. This is due to less ventilation and additional sources of radon and thoron. Radon and thoron decay products, some of them emit an alpha particle, are inhaled and deposit in human respiratory tract, resulting in increased radiological doses and consequently in increased lung cancer risk. It is therefore necessary to assess not only the radon and thoron concentration level but also characteristics of radioactive aerosols bearing radon and thoron decay products.
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Study on Tritium Behavior in the Environment
Tritium (3H or T), a radioactive isotope of hydrogen, is released from nuclear facilities into the environment although the amount and concentration is assessed to be safe. The amount of tritium release is projected to increase due to increasing number of reactors, spent fuel reprocessing plants and fusion reactors. Tritium in the environment can take various chemical forms such as hydrogen gas (HT), tritiated water (HTO) and organically bound tritium (OBT). Since HTO and OBT are easily incorporated into human body, it is important to quantitatively understand migration of tritium, to which both physical factors such as molecular diffusion process and biological factors such as microbial activity and plant physiology relate.
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