Measurement of tritium and carbon-14 in environmental samples, (1)

The measurement of tritium and carbon-14 of natural level has been initiated in many countries since 1950, because they can be applied to age determination. A number of methods have been studied with the development of gas counting and liquid scintillation counting. The author et al. have continued C-14 measurement by means of CO2-filled counters since about fifteen years. The findings on the back-ground and plateau characteristics of the counters are described according to the experiences. Also shielding methods and the preparation of gas samples are reported. The concentration device by electrolysis was made for the tritium measurement aiming at low level counting. Both electrodes for the electrolysis were made of nickel for the reason of the good reproducibility of concentration factor. Since detonating gases are generated during the electrolysis, its explosion has been often reported, but the authors have no experience. As the example of C-14 measurement for environmental samples, there is only the result on the contamination of paddy fields because the authors' purpose of measurement is age determination. In foreign countries, the routine observations of carbon-dioxide in air, foods and human tissues are carrying out. For tritium, the authors have the data on rain from 1961 to 1968. (Wakatsuki, Y.)