Fallout of uranium and plutonium from recent volcanic eruptions

The concentrations of 234U, 235U, 238U in rain water were measured in a total of 102 individual samples which were collected at Fayetteville, Arkansas, from July 1980 through April 1983. A spectacular increase in the heavy isotope of uranium (238U) was observed in the months of July, August (1980); January through April, November and December 1981. This large increase in 238U in rain appeared to have had its origin in the May 1980 eruption of Mount St. Helens. An increase in the concentration of 238U in rain, smaller than 1981, was observed, which seems to have originated from the El Chichon volcano eruption in March 1982, and the spring peak or so-called cycling effect. A striking increase in the average bimonthly concentration of /sup 239,240/Pu occurred during the months of September-October 1980 (15.6 fCi/l) and March-April 1981 (29.4 fCi/l). The excess deposition of /sup 239,240/Pu brought down by the rain at Fayetteville, Arkansas, from March 1980 through December 1982 was found to be 1.01 fCi/cm2. The total amount of /sub 239,240/Pu deposited at Fayetteville, Arkansas, from March through December 1982, was found to be about 30 times higher than the total amount calculated from reported literature values. The excess /sup 239,240/Pu has been attributed to stratospheric /sub 239,240/Pu from nuclear weapons testing prior to the 25th Chinese nuclear test