Differentiating Fukushima and Nagasaki Plutonium from Global Fallout Using 241pu/239pu Atom Ratios: Pu Vs. Cs Uptake and Dose to Biota.

Plutonium (Pu) has been released in Japan by two very different types of nuclear events - the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive Pu-241/Pu-239 atom ratios. In contrast, other typically-used Pu measures (Pu-240/Pu-239 atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of similar to 0.4%-2% in the 0-5 cm soils, similar to 0.3%-3% in earthworms, and similar to 1%-10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the Cs-134,Cs-137 uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (similar to 93% soils, similar to 88% earthworm, similar to 96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher(239)Pu and was distinguished by both Pu-240/Pu-239 and Pu-241/Pu-239 atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of Pu-241/Pu-239 atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.