Plutonium anomaly in nature

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 deg N, 94 deg 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. (author)