The 240Pu/239Pu atom ratio in Chinese soils

Abstract The 240 Pu/ 239 Pu atom ratio is a very effective tool for the identification of the origin of plutonium (Pu) in the soil environment. We examine a dataset of 240 Pu/ 239 Pu atom ratios determined from surface and core soils at 240 sites across China. The data were compiled from 18 separate literature sources from the last 20 years. For the first time the spatial distribution (3 latitude bands and 7 natural regions) of the weighted average 240 Pu/ 239 Pu atom ratios in Chinese soils is investigated. An area to the West of Xining City, shows a weighted average 240 Pu/ 239 Pu atom ratio of 0.167 ± 0.002, lower than that of average global fallout, which likely arises from the addition of local fallout radionuclides from the Chinese nuclear weapon tests at Lop Nor between 1964 and 1980. The Yumen and Jiuquan areas of Northwest China in particular show evidence of very low ratio material from the Chinese nuclear weapon tests. Excluding the impacted area around the test site the weighted average 240 Pu/ 239 Pu ratio of 0.182 ± 0.002 suggests that global fallout is the main source of Pu in most Chinese soils.