Plutonium isotopes in Northern Xinjiang, China: Level, distribution, sources and their contributions

Abstract

Plutonium in the environment has drawn significant attentions due to its radiotoxicity in high concentration and source term linked with nuclear accidents and contaminations. The isotopic ratio of plutonium is source dependent and can be used as a fingerprint to discriminate the sources of radioactive contaminant. 239Pu, 240Pu and 137Cs in surface soil and soil cores collected from Northern Xinjiang were determined in this work. The concentrations of 239,240Pu and 137Cs are in the range of 0.06–1.20 Bq kg−1, and <1.0–31.4 Bq kg−1 (decay corrected to Sep. 2017), respectively, falling in the ranges of global fallout in this latitude zone. The 240Pu/239Pu atomic ratios of 0.118–0.209 and 239,240Pu/137Cs activity ratios of 0.039–0.215 were measured. Among the investigated sites, distinctly lower 240Pu/239Pu atomic ratios of 0.118–0.133 and higher 239,240Pu/137Cs activity ratios of 0.065–0.215 compared to the global fallout values were observed in the northwest part, indicating a significant contribution from other source besides the global fallout. This extra source is mainly attributed to the releases of atmospheric nuclear weapons testing at Semipalatinsk Nuclear Test Site, which was transported by the west and northwest wind through the river valley among mountains in this region. This contribution is estimated to account for 28–43% of the global fallout in the northwest part of Northern Xinjiang. The contribution from the Chinese atmospheric nuclear weapons testing to this region is negligible due to the lack of appropriate wind direction to transport the radioactive releases to this region.