Characterization of the Chemical Composition of Uranium Microparticles with Irregular Shapes Using Standardless Electron Probe Microanalysis and Micro-Raman Spectrometry.

We describe an approach enabling the identification of the elemental composition of uranium microparticles with undefined geometry using standardless quantitative electron probe microanalysis (EPMA) and micro-Raman spectrometry (MRS). The standardless procedure is based on a ZAF peak-to-background quantitative method in combination with Monte Carlo simulations. The experimental X-ray spectra were measured with an energy-dispersive spectrometer attached to a scanning electron microscope. To account for the X-ray intensity loss due to the transmission of electrons in microparticles with irregular shapes, a method was developed enabling the determination of an apparent thickness of the particle by means of the mean distance that electrons travel inside the particle before being transmitted. Size effects were further taken into account by using peak-to-background ratios and performing simulations on a particle with a thickness equal to the apparent thickness. To assess the validity of the standardless procedure in EPMA, weight fractions were determined for NIST homogeneous spherical microparticles of K411 glass and compared to certified ones. The correction of size effects was achieved and lead to accurate quantitative results with absolute relative deviations less than 9%. The model used for the determination of the apparent thickness was validated on the set of spherical K411 particles and enabled us to conduct quantifications on irregularly shaped uranium microparticles. The chemical composition of uranium particles was further investigated using MRS which enabled us to verify the reliability of the results obtained by the standardless approach.

More than Five Percent Ionization Efficiency by Cavity Source Thermal Ionization Mass Spectrometry for Uranium Subnanogram Amounts.

Numerous applications require the precise analysis of U isotope relative enrichment in sample amounts in the subnanogram to picogram range; among those are nuclear forensics, nuclear safeguards, environmental survey, and geosciences. However, conventional thermal ionization mass spectrometry (TIMS) yields U combined ionization and transmission efficiencies (i.e., ratio of ions detected to sample atoms loaded) of less than 0.1% or 2% depending on the loading protocol, motivating the development of sources capable of enhancing ionization. The new prototype cavity source TIMS at ETH Zürich offers improvements from 4 to 15 times in combined ionization and transmission efficiency compared to conventional TIMS, yielding up to 5.6% combined efficiency. Uranium isotope ratios have been determined on reference standards in the 100 pg range bound to ion-exchange or extraction resin beads. For natural U standards, n(235U)/ n(238U) ratios are measured to relative external precisions of 0.5-1.0% (2RSD, 2 < n < 11, conventional source) or 2.0% (2RSD, n = 6, cavity source) and accuracies of 0.2-0.7% (conventional source) or 0.4-0.9% (cavity source). Meanwhile, n(234U)/ n(238U) ratios are determined to relative external precisions of 1.7-3.6% (2RSD, 2 < n < 11, conventional source) or 5.6% (2RSD, n = 6, cavity source) and accuracies of 0.1-2.5% (conventional source) or 0.5-8.3% (cavity source), which would benefit further from in-run organic interference and peak tailing corrections.

Determination of the isotopic composition of single sub-micrometer-sized uranium particles by laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry.

RATIONALE: A multi-collector inductively coupled plasma (MC-ICP) mass spectrometer coupled to a UV ns-laser ablation (LA) system was used to measure uranium isotopic ratios (234 U/238 U, 235 U/238 U and 236 U/238 U) in single uranium particles of various sizes and isotopic compositions, including home-made sub-micrometric natural uranium particles of narrow size distribution (415 ± 60 nm). METHODS: The LA-ICP mass spectrometer was operated in wet plasma conditions thanks to simultaneous injection of the laser aerosol and water vapor through a desolvating nebulizer. The isotopic ratios were corrected for mass bias and gain factors between detectors. The 236 U/238 U ratios were also corrected for the presence of 235 U hydrides and tailing of the 238 U+ peak. RESULTS: 236 U/238 U ratios were successfully measured in micrometer-sized particles from the NBS U050 certified standard material with a 236 U/238 U ratio of ~5 × 10-4 . The analysis of 77 natural uranium sub-µm-sized particles yielded a very good trueness with respect to the expected 234 U/238 U and 235 U/238 U ratios, while the measurement errors for single particles ranged from -2.7% to +2.1% for 235 U/238 U and from -17% to +33% for the 234 U/238 U ratios. Their relative combined standard uncertainties ranged from 3.3% to 32.8% and from 0.4% to 4.0% for 234 U/238 U and 235 U/238 U ratios, respectively. In addition, extremely low detection limits, in the attogram range, were achieved. CONCLUSIONS: This study demonstrates that coupling of a ns-laser ablation system with a MC-ICP mass spectrometer allows measurements of the isotopic composition in natural uranium particles of a few hundreds of nm with very good trueness, average combined standard uncertainties of ~1% for 235 U/238 U ratios and 12% for 234 U/238 U ratios, and detections limits of a few ag for minor isotopes.

Direct Online Determination of Laser-Induced Particle Size Distribution by ICPMS.

The characterization of the aerosol (size, composition, and concentration) generated by Laser Ablation is of great interest due to its impact on the analytical performances when coupled to Inductively Coupled Plasma Mass Spectrometry (ICPMS). The capabilities of High Resolution ICPMS as a direct tool to characterize nanoparticles produced by femtosecond Laser Ablation of pure copper are presented. An analytical protocol, similar to the "single particle ICPMS" technique used to characterize the size distribution of nanoparticles in solution, was developed in order to observe the signals of individual particles produced by a single ablation shot. A Visual Basic for Applications (VBA) data processing was developed to count and sort the particles as a function of their size and thus determine the particle size distribution. To check the reliability of the method, the results were compared to a more conventional technique, namely, Electrical Low Pressure Impaction (ELPI) for 4000 shots. Detection limit for the particles produced by the laser ablation of a copper foil is of a few attograms corresponding to a nanoparticle of 14 nm. The direct online determination of particle size by ICPMS gave similar results than ELPI for copper particles ejected during the ablation shot by shot at a fixed spot, from 1 to 100 shots. Particles larger than 159 nm represented less than 1% of the aerosol whose distribution was centered on 25-51 nm.

Improving Precision and Accuracy of Isotope Ratios from Short Transient Laser Ablation-Multicollector-Inductively Coupled Plasma Mass Spectrometry Signals: Application to Micrometer-Size Uranium Particles.

The isotope drift encountered on short transient signals measured by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) is related to differences in detector time responses. Faraday to Faraday and Faraday to ion counter time lags were determined and corrected using VBA data processing based on the synchronization of the isotope signals. The coefficient of determination of the linear fit between the two isotopes was selected as the best criterion to obtain accurate detector time lag. The procedure was applied to the analysis by laser ablation-MC-ICPMS of micrometer sized uranium particles (1-3.5 µm). Linear regression slope (LRS) (one isotope plotted over the other), point-by-point, and integration methods were tested to calculate the (235)U/(238)U and (234)U/(238)U ratios. Relative internal precisions of 0.86 to 1.7% and 1.2 to 2.4% were obtained for (235)U/(238)U and (234)U/(238)U, respectively, using LRS calculation, time lag, and mass bias corrections. A relative external precision of 2.1% was obtained for (235)U/(238)U ratios with good accuracy (relative difference with respect to the reference value below 1%).

In-SEM Raman microspectroscopy coupled with EDX--a case study of uranium reference particles.

Information about the molecular composition of airborne uranium-bearing particles may be useful as an additional tool for nuclear safeguards. In order to combine the detection of micrometer-sized particles with the analysis of their molecular forms, we used a hybrid system enabling Raman microanalysis in high vacuum inside a SEM chamber (SEM-SCA system). The first step involved an automatic scan of a sample to detect and save coordinates of uranium particles, along with X-ray microanalysis. In the second phase, the detected particles were relocated in a white light image and subjected to Raman microanalysis. The consecutive measurements by the two beams showed exceptional fragility of uranium particles, leading to their ultimate damage and change of uranium oxidation state. We used uranium reference particles prepared by hydrolysis of uranium hexafluoride to test the reliability of the Raman measurements inside the high vacuum. The results achieved by the hybrid system were verified by using a standalone Raman microspectrometer. When deposited on exceptionally smooth substrates, uranyl fluoride particles smaller than 1000 nm could successfully be analyzed with the SEM-SCA system.

Novel insights into Fukushima nuclear accident from isotopic evidence of plutonium spread along coastal rivers.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to important releases of radionuclides into the environment, and trace levels of plutonium (Pu) were detected in northeastern Japan. However, measurements of Pu isotopic atom and activity ratios are required to differentiate between the contributions of global nuclear test fallout and FDNPP emissions. In this study, we used a double-focusing sector field ICP-MS to measure Pu atom and activity ratios in recently deposited sediment along rivers draining the most contaminated part of the inland radioactive plume. Results showed that plutonium isotopes (i.e., (239)Pu, (240)Pu, (241)Pu, and (242)Pu) were detected in all samples, although in extremely low concentrations. The (241)Pu/(239)Pu atom ratios measured in sediment deposits (0.0017-0.0884) were significantly higher than the corresponding values attributed to the global fallout (0.00113 ± 0.00008 on average for the Northern Hemisphere between 31°-71° N: Kelley, J. M.; Bond, L. A.; Beasley, T. M. Global distribution of Pu isotopes and (237)Np. Sci. Total. Env. 1999, 237/238, 483-500). The results indicated the presence of Pu from FDNPP, in slight excess compared to the Pu background from global fallout that represented up to ca. 60% of Pu in the analyzed samples. These results demonstrate that this radionuclide has been transported relatively long distances (∼45 km) from FDNPP and been deposited in rivers representing a potential source of Pu to the ocean. In future, the high (241)Pu/(239)Pu atom ratio of the Fukushima accident sourced-Pu should be measured to quantify the supply of continental-originating material from Fukushima Prefecture to the Pacific Ocean.

Comparison of the fluctuations of the signals measured by ICP-MS after laser ablation of powdered geological materials prepared by four methods.

Sample preparation is a crucial point for quantitative multi-elemental analses by LA-ICP-MS of powdered geological materials. Four different methods are compared in this study with respect to signal stability and intensity as follows: the preparation of glass beads (GlassB) by alkaline fusion method and three grinding and pelletizing methods relying on the use of an organic binder (VanBind, vanillic acid), an adhesive binder (MixGlue, methyl methacrylate) and a sol-gel process for glass formation (SolGel, chemical reaction of tetraethoxysilane), respectively. Sixty elements were analyzed by means of a ns-UV (213 nm) laser ablation system coupled to a single collector sector field ICP-MS with a low or medium mass resolution. Signal stability was found to strongly depend on the sample homogeneity provided by the preparation method. These methods were applied to three geological standard materials (CRM). The following criteria were used to evaluate and compare the methods: (1) proportion of the measurement cycles which are above a given signal intensity threshold (defined here as signal average ± 3 times the standard deviation), (2) signal stability of the analyzed nuclides (internal precision estimated by the relative standard deviations on raw count rates), (3) signal stability of the internal standards added to the samples, (4) external precision estimated by the relative standard deviation over five preparations for each geological CRM. For the majority of the analyzed elements, signals measured for samples prepared with the four methods are reproducible. Specific contamination in one or several elements (Cr, Fe, Co, Ni, Cu, Mo, W, Au and Bi) was observed depending on the sample preparation method. In addition, compared to grinding made with PTFE material, grinding performed with tungsten carbide material was found to produce better homogeneity, especially for the sol-gel and mixing with glue protocols, although some metallic contamination (W and Co) was observed. Thanks to the suppression of grain effects by alkaline melting, the glass bead method systematically provided signal stability and percentage of "over the threshold" close to those of the NIST glasses. This may be explained by the preparation of more homogeneous samples by alkaline melting. Finally, the described methods were found to be reproducible for the majority of the analyzed elements.

240Pu/239Pu isotopic ratio measurements in micrometric Pu and MOX particles using Secondary Ion Mass Spectrometry.

Every accident affecting industrial or nuclear facilities emits micrometric fragments of material into the environment whose elemental and isotopic compositions are characteristic of the process or event. Particle analysis, mainly implemented in the framework of the Non Proliferation Treaty to detect clandestine nuclear activities, provides a powerful tool to identify the origin of the nuclear particulate matter and to assess the environmental impact of nuclear accidents. Initially, particle-scale isotopic analyses aimed at the determination of the U isotopic composition. Now, focus is increasingly given on Pu isotopic measurements to address its origin and potential use. Such measurements are more challenging because of isobaric interferences, including those induced by hydride ions, like 239PuH+ on 240Pu+ and 238UH+ on 239Pu+ in Mixed Oxide (MOX). Such ions are generated during ionization processes by Secondary Ion Mass Spectrometry. Based on a parametric study aiming at the measurement of uranium oxide, uranium carbide and uranium single and double hydride rates, we determined that Pu and U should be detected as elementary ions to limit the impact of such interferences, although mono-oxide ions are more abundant. Thus, we developed an analytical methodology to obtain accurate 240Pu/239Pu atomic ratios both for weapon grade Pu and MOX materials. Hydride rate is first measured in U oxide particles and then applied to correct 240Pu+ and 239Pu+ signals. The relative difference of corrected 240Pu/239Pu isotopic ratios with expected values is reduced by a factor of 4 when measuring weapon grade Pu particles and by a factor of 10-100 when measuring MOX particles containing 1 to 10 wt% of Pu. We also proposed a method to determine the Relative Sensitivity Factor (RSF) based on the decay of Pu in order to quantify the Pu content in MOX samples. The estimated lowest measurable 239Pu/238U atomic ratio in MOX particles is ∼1.6 × 10-3.

Temporal evolution of plutonium concentrations and isotopic ratios in the Ukedo - Takase Rivers draining the Difficult-To-Return zone in Fukushima, Japan (2013-2020).

In 2011, the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident released significant quantities of radionuclides into the environment. Japanese authorities decided to progressively reopen the Difficult-To-Return Zone after the decontamination of priority reconstruction zones. These areas include parts of the initially highly contaminated municipalities located to the north of the FDNPP, including Namie Town, an area drained by the Ukedo and Takase Rivers. Eleven years after the accident, research focused on the spatial distribution of plutonium (Pu) and radiocesium (Cs) isotopes at contrasted individual locations. To complement previous results, the current research was conducted on flood sediment deposits collected at the same locations after major flooding events during eleven fieldwork campaigns organised between 2013 and 2020 at the outlet of the Ukedo and Takase Rivers (n = 22). The results highlighted a global decrease of the Pu and 137Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g-1) to 2020 (4.28 fg g-1). Furthermore, based on the analysis of the 240Pu/239Pu isotopic ratios, the plutonium transiting these rivers (range: 0.166 - 0.220) essentially originated from the global fallout (0.180 ± 0.014 (Kelley et al., 1999)). Sediment showed contrasted properties in the two investigated rivers, which is likely mainly the result of the occurrence of Ogaki Dam on upper sections of the Ukedo River as it strongly impacts the material supply from this river to the Pacific Ocean. A statistical analysis highlighted the strong correlation between Pu activity concentrations and 137Cs activities in both rivers, confirming that both radionuclides are transported with a similar pathway. Despite it was detected early after the accident (2011-2013), the current research demonstrates that plutonium originating from FDNPP is no longer detected in these rivers draining the Difficult-To-Return Zone at the onset of the reopening of the area to its former inhabitants.

Production and characterization of plutonium dioxide particles as a quality control material for safeguards purposes.

Plutonium (Pu) dioxide particles were produced from certified reference material (CRM) 136 solution (CRM 136-plutonium isotopic standard, New Brunswick Laboratory, Argonne, IL, U.S.A., 1987) using an atomizer system on December 3, 2009 after chemical separation of americium (Am) on October 27, 2009. The highest density of the size distribution of the particles obtained from 312 particles on a selected impactor stage was in the range of 0.7-0.8 µm. The flattening degree of 312 particles was also estimated. The isotopic composition of Pu and uranium (U) and the amount of Am were estimated by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and α-spectrometry. Within uncertainties the isotopic composition of the produced particles is in agreement with the expected values, which were derived from the decay correction of the Pu isotopes in the CRM 136. The elemental ratio of Am to Pu in the produced particles was determined on the 317th and 674th day after Am separation, and the residual amount of Am in the solution was estimated. The analytical results of single particles by micro-Raman-scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry (EDX) indicate that the produced particles are Pu dioxide. Our initial attempts to measure the density of two single particles gave results with a spread value accompanied by a large uncertainty.

240Pu/239Pu signatures allow refining the chronology of radionuclide fallout in South America.

Atmospheric nuclear tests (1945-1980) have led to radioactive fallout across the globe. French tests in Polynesia (1966-1974) may influence the signature of fallout in South America in addition to those conducted by USA and former USSR until 1963 in the Northern hemisphere. Here, we compiled the 240Pu/239Pu atom ratios reported for soils of South America and conducted additional measurements to examine their latitudinal distributions across this continent. Significantly lower ratio values were found in the 20-45° latitudinal band (0.04 to 0.13) compared to the rest of the continent (up to 0.20) and attributed to the contribution of the French atmospheric tests to the ultra-trace plutonium levels found in these soils. Based on sediment cores collected in lakes of Chile and Uruguay, we show the added value of measuring 240Pu/239Pu atom ratios to refine the age models of environmental archives in this region of the world.

Application of nanosecond-UV laser ablation-inductively coupled plasma mass spectrometry for the isotopic analysis of single submicrometer-size uranium particles.

For the first time, laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) was used to carry out isotopic measurement on single submicrometer-size uranium particles. The analytical procedure was applied on two particle-containing samples already analyzed in the same laboratory by established techniques for particle analysis: combination of the fission track technique with thermo-ionization mass spectrometry (FT-TIMS) and secondary ion mass spectrometry (SIMS). Particles were extracted from their initial matrix with ethanol and deposited on a polycarbonate disk where they were fixed in a layer of an organic compound (collodion). Prior to the isotopic analysis, particles were precisely located on the disk's surface by scanning electron microscopy (SEM) for one sample and using the fission track technique for the other sample. Most of the particles were smaller than 1 µm, and their (235)U content was in the femtogram range. (235)U/(238)U ratios were successfully analyzed for all located particles using a nanosecond-UV laser (Cetac LSX 213 nm) coupled to a quadrupole-based ICPMS (Thermo "X-Series II"). LA-ICPMS results, although less precise and accurate (typically 10%) than the ones obtained by FT-TIMS and SIMS due to short (20-40 s), transient, and noisy signals, are in good agreement with the certified values or with the results obtained with other techniques. Thanks to good measurement efficiency (~6 × 10(-4)) and high signal/noise ratio during the analysis, LA-ICPMS can be considered a very promising technique for fast particle analysis, provided that uranium-bearing particles are fixed on the sample holder and located prior to isotope measurement.

A new method for determining 236U/238U isotope ratios in environmental samples by means OF ICP-MS/MS.

The 236U/238U isotope ratio is a widely used tracer, which provides information on source identification for safeguard purposes, nuclear forensic studies and environmental monitoring. This paper describes an original approach to determine 236U/238U ratios, below 10-8, in environmental samples by combination of ICP-MS/MS for 236U/238U ratio and multiple collector ICPMS measurements for 235U/238U and 234U/235U isotope ratios. Since the hydride form of UO+ (UOH+) is less prone to occur than UH+, we were focused on the oxidised forms of uranium in order to reduce hydride based-interferences in ICP-MS/MS. Then, in-cell ion-molecule reactions with O2 and CO2 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 evaluated using five different desolvating systems. The best conditions, using an Apex Ω or an Aridus system, produced uranium oxide hydride rate (235U16O1H+/235U16O+) of about 10-7 with O2 in the collision cell. The method was validated through measurements of two certified IRMM standards with 236U/238U isotope ratio of 1.245 × 10-7 and 1.052 × 10-8, giving results in agreement with certified reference values. The relative standard deviations on seven independent measurements for each standard were respectively of 1.5% and 6.2%. Finally, environmental samples corresponding to sediments from the radioactive contamination plume emitted by the Fukushima Daiichi Nuclear Power Plant accident were analysed after a well-established uranium chemical separation procedure. 236U/238U atomic ratios between 1.5 × 10-8 and 7 × 10-9 were obtained with a level accuracy lower than 20%.

Colloidal mobilization from soil and transport of uranium in (sub)-surface waters.

An analytical methodology was developed to characterize the colloidal distribution of trace elements of interest in environmental waters sampled in a same site and enables the different colloidal distributions from waters to be compared. The purpose was to provide consistent information related to the origin and nature of colloids responsible for the transport of trace element(s). The work was motivated by the observed enhanced mobility of uranium in soil. The colloidal size continuum was investigated by a multi-technique approach involving asymmetric flow field-flow fractionation (AF4) coupled with ultraviolet spectroscopy (UV), multi angle light scattering (MALS), and atomic mass spectrometry (ICPMS). To take into consideration the size and shape variability specific to each sample, the size distributions were established from the gyration radii measured from MALS, also considering the size information from standard nanospheres fractionated by AF4. A new parameter called "shape index" was proposed. It expresses the difference in hydrodynamic behavior between analytes and spherical particles taken as reference. Under AF4 diffusion conditions, it can be considered as an evaluator of the deviation from the sphericity of the fractionated analytes. AF4-UV-MALS-ICPMS enabled the dimensional and chemical characteristics of the colloidal size continuum to be obtained. As a "proof of concept", the developed methodology was applied at a field scale, in a reference study site. In order to have a "dynamic understanding", the investigation was based on the joint characterization of colloids from surface waters and soil leachates from static and dynamic processes. In the water samples of the study site, the continuum of gyration radius ranged from a few nanometers up to 200 nm. Colloids containing iron, aluminum, and organic carbon were involved in the uranium transport in the soil column and surface waters. The colloidal uranium concentration in the surface water increased from the upstream location (approximately 13 ng (U) L-1) to the downstream location (approximately 60 ng (U) L-1).

Reconstruction of uranium and plutonium isotopic signatures in sediment accumulated in the Mano Dam reservoir, Japan, before and after the Fukushima nuclear accident.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in Japan resulted in a major release of radionuclides into the environment. Compared to other radionuclides, few studies have investigated the fate of actinides in the environment. Accordingly, this research investigates the Pu composition in soil samples collected in paddy fields before and after the accident. Furthermore, the vertical distributions of Pu and U isotopic signatures, along with 137Cs activities, were measured in a sediment core collected in the Mano Dam reservoir, in the Fukushima Prefecture. Changes in the relative contributions of the major actinide sources (global fallout or FDNPP derived fallout) were investigated in sediment deposited in the reservoir. The distinct peak observed for all Pu isotope ratios (240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu) and for 137Cs concentrations in the sediment core was attributed to the Fukushima fallout, and coincided with the maximum atomic contribution of only 4.8 ±â€¯1.0% of Pu from the FDNPP. Furthermore, 236U/238U ratios measured in the sediment core remained close to the global fallout signature indicating there was likely no U from the FDNPP accident detected in the sediment core. More research is required on the environmental dynamics of trace actinides in landscapes closer to the FDNPP where there are likely to be greater abundances of FDNPP-derived Pu and U.

Plutonium isotopic signatures in soils and their variation (2011-2014) in sediment transiting a coastal river in the Fukushima Prefecture, Japan.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted in a significant release of radionuclides that were deposited on soils in Northeastern Japan. Plutonium was detected at trace levels in soils and sediments collected around the FDNPP. However, little is known regarding the spatial-temporal variation of plutonium in sediment transiting rivers in the region. In this study, plutonium isotopic compositions were first measured in soils (n = 5) in order to investigate the initial plutonium deposition. Then, plutonium isotopic compositions were measured on flood sediment deposits (n = 12) collected after major typhoon events in 2011, 2013 and 2014. After a thorough radiochemical purification, isotopic ratios (240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu) were measured with a Multi-Collector Inductively Coupled Mass Spectrometer (MC ICP-MS), providing discrimination between plutonium derived from global fallout, from atmospheric nuclear weapon tests, and plutonium derived from the FDNPP accident. Results demonstrate that soils with the most Fukushima-derived plutonium were in the main radiocaesium plume and that there was a variable mixture of plutonium sources in the flood sediment samples. Plutonium concentrations and isotopic ratios generally decreased between 2011 and 2014, reflecting the progressive erosion and transport of contaminated sediment in this coastal river during flood events. Exceptions to this general trend were attributed to the occurrence of decontamination works or the remobilisation of contaminated material during typhoons. The different plutonium concentrations and isotopic ratios obtained on three aliquots of a single sample suggest that the Fukushima-derived plutonium was likely borne by discrete plutonium-containing particles. In the future, these particles should be isolated and further characterized in order to better understand the fate of this long-lived radionuclide in the environment.

Comparing results of X-ray diffraction, µ-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise.

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, µ-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO2 in two materials, and as a mixture of UO2, U3O8 and an intermediate species U3O7 in the third material.

Development toward a double focusing isotopic separator for noble gas isotope enrichment.

A double focusing sector field mass filter used in Nier-Johnson geometry has been built in order to perform Kr isotope enrichment for 81 Kr and 85 Kr isotopes. The principle consists in implanting Kr+ ions accelerated at 7 keV in Al foils after separation using the magnetic sector. A specific ion source has been designed capable of generating high Kr+ ion beams (>0.5 µA) to transfer into the collecting Al foils in 3 to 5 h significant fractions of large Kr samples (1015 to 1016 atoms) initially introduced in the instrument. Implanted Kr isotopes can be further selectively released from the Al foil by surface ablation using an infrared laser beam. Implantation yields and enrichment factors are measured using a conventional mass spectrometer. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation of uranium-colloid interactions in soil by dual field-flow fractionation/capillary electrophoresis hyphenated with inductively coupled plasma-mass spectrometry.

This paper deals with the study of uranium-colloid interactions in a carbonated soil. The work is focused on the immediately available fraction obtained after a leaching process, according to a normalized batch method. In order to characterize the different colloidal carriers, Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) coupled to different detectors (UV, Multi Angle Laser Light Scattering (MALLS) and Inductively coupled Plasma-Mass Spectrometry (ICP-MS)) was used. The colloidal carriers are mainly inorganic particles (carbonated particles and clays) mixed with organic substances. Furthermore, dissolved and colloidal uranium species in the leaching solutions were monitored by Capillary Electrophoresis (CE) coupled to ICP-MS, in order to investigate the uranium/colloids interactions. According to the first results, uranium fate in this specific soil is controlled by sorption/desorption phenomena, strongly pH dependent.