Studies on the tritium measurement in rain and ground water in Japan

Tritium in the rain water and ground water in Osaka, Japan was investigated since 1956. Average tritium concentration in rain water was found to decrease from about 200 TU in 1965 to 30 TU in 1977, repeating seasonal variations. These values were compared with IAEA's data of Ottawa, Vienna, Teheran, Pohang, Tokyo and Guam. The average values of Osaka, Tokyo and Pohang are about the same and are roughly about one half of the values of Ottawa and Vienna in spite of the locations of nearly the same latitude. 90Sr and 137Cs concentration in the same rain water in Osaka were also determined to be about 1 pCi/l and seasonal variations almost parallel to those of tritium were observed. Tritium, 90Sr and 137Cs in the ground water drawn up from the well 350 meter deep were assayed to be about 5 TU, 0.01 pCi/l and 0.05 pCi/l respectively. The results of measurement of sea water, river water and hot spring water in Japan are also introduced. Tritium enrichment process for low level tritium measurement using electrolysis is introduced and the variations of separation factor due to several electrolytic conditions are discussed. It was found that the separation factor of tritium to protium, β, decreases when the temperature of electrolytic solution rises and electric current density decreases. The value of β decreases abruptly when electrolyte concentration is below 1%. (author)