1993 年 35 巻 2 号 p. 87-93
The tritium concentrations in rain water collected in Fukuoka, Japan, from April 1987 to July 1991, were measured with the combination of low-level liquid scintillation counting and electrolytic en-richment of tritium in water. The tritium concentration of each rainfall (264 samples) showed the large fluctuation from 0.06 to 3.39 Bq/l. The tritium concentration in rain was significantly affected by the weather conditions. The frequency distributions of tritium concentrations in rain water were shifted to higher side in March, April, May and December. Higher tritium concentrations than 2.0 Bq/l were observed only in March, April and May, when air mass moved dominantly from the Asian Continent to Fukuoka. The annual average concentrations were no longer decreased after 1987 in Fukuoka.