ABSTRACT

The ²³⁹Pu/²³⁸U ratios are reexamined in volcanic ashes and rock, uranium mineral and other contemporary terrestrial samples and also in the atmospheric samples. This ratio in rain samples collected at Fayetteville (36°N, 94°W), Arkansas, reaches up to 10^-5 (atom/atom), which is about 2 orders of magnitude higher than those of volcanic ashes and rock and about five or six orders of magnitude higher than the ²³⁹Pu/²³⁸U ratio of 10^-12 (atom/atom) typical of uranium minerals. The data obtained from our measurements indicate that the high ²³⁹Pu/²³⁸U ratios observed in this contemporary terrestrial samples are due to fallout contaminations.