Suchergebnisse

International audience The $^{236}$U/$^{238}$U isotope ratio is a widely used tracer, which provides information on source identification forsafeguard purposes, nuclear forensic studies and environmental monitoring. This paper describes an originalapproach to determine $^{236}$U/$^{238}$U ratios, below 10$^{−8}$, in environmental samples by combination of ICP-MS/MS for $^{236}$U/$^{238}$U ratio and multiple collector ICPMS measurements for $^{235}$U/$^{238}$U and $^{234}$U/$^{235}$U isotope ratios.Since the hydride form of U$^+$ (UOH$^+$) is less prone to occur than UH$^+$, we were focused on the oxidisedforms of uranium in order to reduce hydride based-interferences in ICP-MS/MS. Then, in-cell ion-moleculereactions with O$_2$ and CO$_2$ were assessed to detect the uranium isotopes in mass-shift mode (Q1: U$^+$ → Q2:UO$^+$). The performances in terms of UO$^+$ sensitivity and minimisation of hydride form of UO$^+$ were evaluatedusing five different desolvating systems. The best conditions, using an Apex $\Omega$ or an Aridus system, produceduranium oxide hydride rate ($^{235}$U$^{16}$O1H$^+$/$^{235}$U$^{16}$O+) of about 10$^{-7}$ with O$^2$ in the collision cell.The method was validated through measurements of two certified IRMM standards with $^{236}$U/$^{238}$U isotoperatio of 1.245×10$^{17}$ and 1.052×10$^{-8}$, giving results in agreement with certified reference values. The relativestandard deviations on seven independent measurements for each standard were respectively of 1.5% and6.2%. Finally, environmental samples corresponding to sediments from the radioactive contamination plumeemitted by the Fukushima Daiichi Nuclear Power Plant accident were analysed after a well-established uraniumchemical separation procedure. $^{236}$U/$^{238}$U atomic ratios between 1.5×10$^{-8}$ and 7×10$^{-9}$ were obtained with a level accuracy lower than 20%.

International audience The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident released limited amounts of actinides on soils of Japan. Characterisation of these particles is essential to determine the fate of actinides in the environment. The method presented in this paper, based on α-tracks detections, microscope observations and mass-spectrometry measurements, was designed to identify and characterize actinide-bearing particles in soil samples. The method was tested on a road dust sample collected in the main radioactive plume of the Fukushima region. Accordingly, α-tracks detection was demonstrated to provide a powerful technique to localise these particles and prepare their morphological, elemental and isotopic characterization.

Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km2 radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset that can be accessed at https://doi.pangaea.de/10.1594/PANGAEA.928594 compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations during 16 fieldwork campaigns conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.