| The concentrations of ('234)U, ('235)U, ('238)U 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 (('238)U) was observed in the months of July, August (1980); January through April, November and December 1981. This large increase in ('238)U in rain appeared to have had its origin in the May 1980 eruption of Mount St. Helens. An increase in the concentration of ('238)U 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. The excess deposition of ('238)U brought down by the rain and snow at Fayetteville, Arkansas, from March 1980 through December 1982, was found to be 3.13 fCi/cm('2).;The concentrations of ('238,239,240)Pu were measured in 101 individual rain samples which were collected at Fayetteville, Arkansas, during the period from January 1981 through April 1983. A striking increase in the average bimonthly concentration of ('239,240)Pu occurred during the months of September-October 1980 (15.6 fCi/l) and March-April 1981 (29.4 fCi/l). The increase in the ('239,240)Pu concentration in rain occurred just about the time the fission products (('89,90)Sr) from the 25th Chinese nuclear test appeared at Fayetteville, Arkansas. The excess deposition of ('239,240)Pu brought down by the rain at Fayetteville, Arkansas, from March 1980 through December 1982 was found to be 1.01 fCi/cm('2). The total amount of ('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 ('239,240)Pu has been attributed to stratospheric ('239,240)Pu from nuclear weapons testing prior to the 25th Chinese nuclear test. Also, the spring peak effect on ('238)Pu, ('239,240)Pu in rain suggested by Rao (1978) was confirmed. |
