Nationwide survey and behavior of tritium in air in China

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A nationwide survey of tritium in water vapor has been carried out in China for providing data used for analyzing regional scale behaviors of atmospheric tritium in East Asia.Besides the usual active method using motive power, a newly developed passive method using no pump was used for sampling water vapor with molecular sieves.An apparatus for withdrawing water from absorbed vapor was constructed and installed at Laboratory of Industrial Hygiene, Ministry of Public Health, Beijing, China. The distillation of withdrew water sample and tritium radioactivity measurement with a liquid scintillation counter have been made at the Laboratory.Sampling of water vapor by the passive method was carried out every two months from June 1992 to August 1993 at 13 cities in China and 5 cities in Japan (Sapporo, Sendai, Nagoya, Kumamoto, Naha).Results of measurement are as follows : 1) Regional distributions of tritium in water vapor in East Asia were obtained every two months. A distribution for annual mean value was also obtained. 2) At Urmuchi and Lanchow, most high annual mean concentration of about 15 Bq/l was observed. The next high group (8-11 Bq/l) includes Harbin, Chanchun, Beijing, Sian, Lhasa, and Wuchang and Chentu follows the group. Concentrations at coastal region (Hangchow, Fuzhou, Sinsen) show low level, and five points in Japan belong the most low level group (1-2 Bq/l). 3) From the regional distribution map, we can see both inland effect and latitude effect. The effect of past nuclear explosion test should be studied later.Sampling by the active method had been made every two days for ten days in each season at Beijing, Lanchow and Fuzhou. Analyzing some date by using two-layer trajectory model, we got fairly good agreement between the calculated concentration level and measured one.