Mass isotopic composition of global fall-out plutonium in soil

The mass isotopic content of fall-out plutonium in soil samples collected from around the world in 1970 and 1971 showed some variability which correlated with the location of nuclear weapons test sites. Omitting local effects, the global mean ratios of 240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu are 0.176+-0.014, 0.0086+-0.0017 and 0.0044+-0.0011, respectively, corrected to January 1971. Such isotopic data provide the most sensitive technique to resolve mixtures of fall-out plutonium with plutonium from a second source. From these data, the 241Am/sup(239,240)Pu activity ratio of integrated fall-out on the earth's surface can be estimated and will peak at 0.42 in the year 2037. (author)