Research on development of high precision monitoring techniques for radon and thoron in environment

In the research on the mass transfer in natural environment, as the substance, of which the property for index is expected, there is radon. Radon is a rare gas element positioned next to radium in the natural decay series from the parent nuclides of uranium, thorium and actinium, and the isotopes, radon, thoron and actinon are formed, of which the half life is 3.8 days, 55s and 3.9s, respectively. Radon is chemically inert, and easy to detect as it emits radiation, therefore, it has been utilized as tracer variously. In this research, it is aimed at to elucidate in detail the behavior of radon and thoron in environment, and to develop the high precision monitoring techniques for radon and thoron which become necessary for the advanced utilization as tracer in hydrology, applied geology and environmental engineering. As for the high precision measuring techniques for very low level radon and thoron in environment, polonium with short life is selected from the daughter nuclides in the decay series, and using a liquid scintillator as the detector, only two radiations continuing in short time are counted. The establishment of time interval discrimination method and the development of radon and thoron monitoring techniques are reported. (K.I.)