Time variations of artificial radionuclide concentrations in the air over Japan since 1974

Deposition of 137Cs, 144Ce and other gamma-ray emitting nuclides to the ground level has been studied from December 1973 at Nagoya, Japan (35deg N, 137deg E). The Chinese nuclear weapons tests were the major source of fission produced nuclides till May 1986, and the thermonuclear explosion of November 17, 1976 made the largest contribution to the stratospheric inventory. Short lived nuclides like 140Ba, 141Ce and 103Ru were detected after small scale nuclear tests, but they tended to deposit to the ground rapidly. Analyses of the experimental results gave tropospheric residence times and other information concerning the movements of the debris in the air. The Soviet reactor accident at Chernobyl (April 26, 1986) brought over Japan more activities than any recent nuclear weapons tests. 137Cs concentration in the air increased by at least three orders of magnitude, and seemed to exceed the highest value ever experienced in this country. Complex transport behaviors of the Chernobyl debris in the atmosphere were observed. (orig.)