Search

International audience; On account of the virtual absence of 236U in nature and its abundance closely related to its provenance, the 236U/238U ratio has been commonly employed as a tracer to provide information in source identification for safeguard purposes, nuclear forensic studies and environmental monitoring. Due to their high performance capabilities, ICP-MS techniques are currently the most widely employed to perform radionuclide determination. However, in the case of 236U and due to its very low relative abundance, its determination is limited by the formation of 235U1H+ in the plasma and by the influence of the tail of the major isotope 238U (abundance sensitivity).In this work, we present an approach based on the ICP-MS/MS technology to determine 236U/238U ratios in environmental samples. The combination of two quadrupole-based mass filters, before (Q1) and after (Q2) the cell, in the MS/MS configuration provides abundance sensitivity values lower than 10-10, avoiding the influence of the 238U tail. In order to reduce the influence of the hydridebased interferences, different desolvation systems have been evaluated in relation to the sensitivity and the hydride rate obtained. In-cell ion-molecule reactions with O2 and CO2 have also been assessed to detect the uranium isotopes in mass-shift mode (Q1 U+ et61664; Q2 UO+). Best conditions provided a hydride rate value (235U16O1H+/235U16O+) in the order of 10-7. Finally, the methodology was validated with IRMM certified standards, and successfully applied to the determination of 236U/238U ratios in U samples from soils originating from the radioactive contamination plume caused by the Fukushima Daiichi Nuclear Power Plant accident. Ratios down to 10-9 have been obtained with precisions lower than 20.

International audience

International audience; La détermination précise des compositions élémentaires et isotopiques dans des échantillons nucléaires est indispensable pour la gestion des combustibles nucléaires et des déchets radioactifs. Cette détermination isotopique et élémentaire porte notamment sur l'uranium, le plutonium et les lanthanides et est effectuée par spectrométrie de masse après séparations chimiques afin d’éliminer les interférences isobariques. L'Électrophorèse capillaire est une technique séparative particulièrement attractive pour ces applications, du fait des très hautes efficacités, des courts temps d'analyse et des micro volumes mis en jeu. Des études menées précédemment au laboratoire ont démontré la faisabilité de séparations U/Pu/Lanthanides et de séparations U/Th en utilisant un électrolyte d'acide acétique et en couplage direct avec un spectromètre de masse Multi-collecteurs a source plasma. La complexité et la diversité des échantillons nucléaires imposent un suivi de la spéciation des éléments d’intérêts dans les conditions développées afin de garantir le succès des analyses. L’étude de spéciation qui sera présentée ici a permis d'expliquer les facteurs influençant le comportement électro-optique des éléments d’intérêt. Ces études de spéciation peuvent être étendues a d'autres électrolytes afin de développer des séparations pour les éléments présents dans les échantillons nucléaires.

International audience; In surface microanalysis with sampling by laser ablation (LIBS, LA-ICP-OES or LA-ICP-MS methods), spatial resolution is determined by laser beam diffraction limits (of the order of a laser wavelength) and thermal diffusion of a deposited heating energy during laser pulse duration (proportional to the square root of the pulse duration and matter diffusivity). Being limited by these features of a laser beam and heating energy, the best LIBS spatial resolution (the crater diameter) of 1 µm was obtained by ablation with the laser pulses of 266 nm wavelength and 4 ns duration [1-2]. One of the ways to improve spatial resolution of microanalysis may be suggested as the use of laser pulses of a lower wavelength ( 266 nm) and shorter pulse durations (ps and fs). Other ways to improve spatial resolution of surface analysis is laser ablation with a highly localized electromagnetic field produced by a tip near-field enhancement. In our studies, a tip of an atomic force microscope (AFM) was illuminated by the laser pulses of 266 nm wavelength and 4 ns duration, thus producing the craters of 100 nm diameters and of some nanometers of depth with Si-, Au- and Ta-samples [3]. The experiments were followed by extensive multi-parametric theoretical studies to analyze the effect of both matter properties (absorption, thermal conductivity and capacity) and electromagnetic field parameters (spatial distribution and pulse duration) on the resulted temperature field distribution T(r, t). The simulations were made with a home-developed “3D+t” heating model [4]. The simulation results [5] with particular features of solid sample heating by highly spatially localized laser field (10-100 nm) will be presented and discussed.

International audience; A method of near-field (NF) laser ablation for sampling of solids with a nm resolution was developed and applied. The method is based on the coupling of nanosecond or femtosecond laser pulses with an Atomic Force Microscope (AFM). The technique uses a tip enhancement effect obtained by interaction of laser radiation with a tip of the AFM maintained a few nm above a sample surface. In our experiments, craters of about 100 nm in diameter and a few nm in depth were obtained with a single laser pulse on gold and silicon samples. The elemental or isotope content of the ablated matter may be analyzed by a mass spectrometer with inductively coupled plasma source (ICP-MS). An electrostatic model of the NF created by an ellipsoidal tip with a coating was used in NF heating and ablation calculations. It allows one to take into account the effect of possible plasmonic resonance (both in the tip and the surface under study) on the NF enhancement factor. A two-temperature model of electron and lattice heating was used for temperature calculations for both heating and ablation regimes. A multi-parametric study was made to understand the effect of different experimental parameters (laser fluence, tip-to-sample distance, sample and tip nature) on NF laser ablation efficiency, crater dimensions and amount of ablated material. The developed combined model of the NF heating and ablation was used to test calculations and to study different interaction features. Numerical simulations of the NF localized heating with a 3-D code have offered a good explanation of nm crater diameters obtained in the experiments.

International audience

National audience; Dans le cadre du recyclage des matières valorisables, des procédés de séparation par extraction liquide-liquide ont été développés au CEA pour extraire sélectivement certains radioéléments contenus dans des solutions de combustibles nucléaires uses. L'analyse de la spéciation exhaustive de ces radioéléments, a différents points clefs des procédés, est essentielle pour acquérir des données fondamentales, en vue d'évaluer/améliorer leurs performances et d'approfondir la compréhension des mécanismes fondamentaux les régissant. Dans ce travail, le couplage entre la chromatographie d'interaction hydrophile (HILIC) [1] et la spectrométrie de masse a source d'ionisation électrospray (ESI-MS) ainsi que les informations de spéciation obtenues seront présentés. Une combinaison phase stationnaire/phase mobile a été définie dans de précédents travaux menés au laboratoire pour séparer des complexes de lanthanides a ligands acides polyaminocarboxylique (EDTA, DTPA) en mode isocratique. Sur la base de ces conditions, l'objectif est de minimiser les volumes d'effluents générés tout en conservant des séparations efficaces et rapides. Parmi les approches existantes pour répondre a cet objectif, la diminution des paramètres géométriques des colonnes (longueur, diamètre interne et taille des particules) et l'utilisation de colonnes remplies de particules superficiellement poreuses (SPP) ont été sélectionnées. Les conditions permettant d'obtenir le meilleur compromis entre performance de séparation, temps d'analyse et consommation de solvants seront discutées. Enfin, le couplage simultané entre la chromatographie HILIC et deux techniques de spectrométries de masses a source d'ionisation d'électrospray (ESI) et a source plasma couplage inductif (ICP), implante en boite a gants pour l'analyse de la spéciation exhaustive d'éléments radioactifs sera presenté.[1] L. Beuvier; C. Bresson; A. Nonell; L. Vio; N. Henry; V. Pichon; F. Chartier. Simple separation and characterization of lanthanidepolyaminocarboxylic acid complexes by HILIC ESI-MS. RSC Adv. 2015, 5 (113), 92858-92868.

International audience

International audience

International audience; To satisfy the growing demands of modern science and industry, laser ablation methods are under continuous development. The development of laser ablation methods has significantly expanded the scope of their applications for modern laser-assisted micro and nanotechnologies. In particular, in our studies on near-field laser ablation, the possibility to perform laser ablation and surface processing with a nanometric resolution was demonstrated with laser field enhancement near a tip of an atomic-force microscope. Laser ablation, in our case, may be regarded as a result of the local near-field heating of a sample surface. Laser ablation efficiency and accuracy are affected by both the sample properties (thermal diffusivity, absorption coefficient, etc.) and the near-field parameters (spatial distribution, wavelength, laser pulse duration, tips nature and dimension, etc.). The modeling of the temperature distribution resulting from the near-field heating of the sample surface may be seen as an appropriate procedure to analyze these complex multi parametric effects and corresponding interrelations. The paper presents the results on the modeling for the near-field heating of metal or semiconductor surfaces (gold, tantalum and silicon wafer) along with those obtained experimentally with nanosecond laser pulses (4 ns, 266 nm, 10 Hz, linear p-polarization) and an atomic-force microscope in air, under normal conditions. The properties of nanometer scale craters are in good correlation with the model predictions. The possible improvements of the near-field ablation with a femtosecond laser will be discussed.

International audience; A near field laser ablation inductively coupled plasma mass spectroscopic method (NF-LA-ICPMS) was developed for chemical analysis at sub-micrometric scale. This analytical technique combines a nanosecond laser, an Atomic Force Microscope (AFM), and a high resolution ICP-MS. In order to improve the spatial resolution of the laser ablation process, the near field enhancement effect was applied by illuminating the apex of a conductive sharp tip of the AFM by a laser beam. The laser energy was kept below the sample ablation threshold, and a distance of a few nanometers (5 to 30 nm) was maintained between the tip and the surface sample. The interaction between the illuminated tip and the sample surface enhances locally the incident laser irradiance and leads to the ablation process.

National audience; La caracterisation isotopique des elements presents apres irradition dans les combustibles est d'une importance majeure pour la validation des codes de calculs neutroniques ou l'acces a des donnees nucleaires de bases. Le protocole actuel au laboratoire pour l'acquisition de donnees elementaires et isotopiques dans ces echantillons necessite plusieurs etapes de separation par chromatographie liquide. Dans une premiere etape, l'uranium (U), le plutonium (Pu) et les Produits de Fission (dont les lanthanides) sont separes puis les fractions purifiees d'U et de Pu sont analysees par spectrometrie de masse. L'objectif de cette etude est le developpement d'une separation U/Pu/lanthanides (Ln) par methode electrophoretique afin de minimiser les volumes d'effluents et les temps d'exposition aux echantillons radioactifs. La separation est couplee a une detection par spectrometrie de masse a source plasma (ICP-MS). Dans cette etude preliminaire, le thorium(IV) a servi d'analogue chimique du Pu(IV). Quatre electrolytes/complexants ont ete selectionnes pour l'etude de la separation par electrophorese capillaire l'acide acetique, l'acide 2,2-hydroxylmethylbutyrique (HMBA), l'acide formique et l'acide malonique. L'acide acetique s'est revele etre l'electrolyte/complexant le plus adapte pour separer l'U, le Th et les Ln. Il permet d'obtenir une plus grande difference de mobilite entre l'U et le Th que l'HMBA ou l'acide formique. De plus, avec l'acide acetique, l'U et le Th peuvent etre separes tout en etant maintenus sous forme cationique, alors que l'acide malonique forme des complexes anioniques. Dans un second temps, une methode de preconcentration des analytes a ete developpee. Elle permet de moduler les profils et les temps d'elution des analytes afin d'obtenir un signal plus adapte pour une quantification precise par ICP-MS. Cette separation sera ensuite transposee en boite a gants sur un microsysteme separatif couple a un ICP-MS-MC pour des mesures isotopiques en ligne de l'U et du Pu ou pour la datation (U-Th) de materiaux nucleaires.

National audience

International audience

International audience

International audience

International audience; In the field of nuclear waste management, actinides and lanthanides speciation studies are mainly carried out by chromatographic techniques, involving hydro-organic mobile phases. Introduction of such matrices into ICP sources is complex and results in ICP analytical performances degradation, such as plasma instabilities, sensitivity losses, spectral and non-spectral interferences, contaminations, cone and injector orifices clogging and even extinction. Technical constraints induced by nuclearized spectrometers, mandatory to handle radioactive samples, render this introduction even more challenging.Various introduction devices are commercialized to address the issue of liquid matrices introduction in ICP with the aim to improve the analytical performances, while facilitating the experiments (high plasma tolerance, robust conditions, etc.). Additional operating parameters optimization is needed to conserve the analytical performances using such matrices. The goal of this study is first to better understand the effects and interactions of the operating parameters on signal sensitivity and stability, obtained for lanthanides in hydro-organic matrices involving various amounts of acetonitrile, hardly compatible with ICP sources. For that, a Peltier-cooled cyclonic spray chamber with O2 introduction port (PC3, Elemental Scientific) has been chosen. Then, three introduction devices with different designs and adapted to nuclear instrumentations, have been used whilst remaining easy to handle a cyclonic spray chamber (considered as the basic configuration), the PC3 and a desolvation device (Apex from Elemental Scientific). These devices are compared according to the maximum amount of organic matrices able to be introduced in ICP-MS and regarding robust analytical performances; the sensitivity and stability measured for each analyte; and finally, their ease-of-use.

International audience; The measurement of U and Pu isotope ratios is of prime interest in nuclear research fields particularly for the management of radioactive waste. One of the major drawbacks in analysing Pu isotopes is the occurrence of 238U–238Pu isobaric interference. In this work we propose to suppress this interference by adding CO2 as a reactive gas in the collision-reaction cell of the MC-ICPMS. We have demonstrated that the different reactivities of Pu andUtowards CO2 gas allow accurate and precise Pu andUisotopic measurements on Pu+ and UO2 + forms, by using two different CO2 gas flow rates: 0.4 mL min1 for Pu+ and 1.5 mL min1 for UO2 +. Parameters like optimum CO2 gas flow in the cell, oxides isotope abundance, instrumental mass bias and memory blank, were carefully evaluated and corrected. The developed analytical method was validated using a transmutation 235U target sample irradiated in the Phenix French fast neutron reactor. A good agreement between isotope ratios of U and Pu measured with CO2 in the cell and U and Pu measured after chemical separation was obtained. The relative difference of the average isotope ratio values between the chemically purified fraction and the direct measurements using CO2 was found to be 0.38% and 0.11% for U and Pu, respectively.

International audience; Architectural morphology is an important factor for the prediction of soundscapes and noise propagation in urban areas. As in room acoustics, the sound field in a street is characterized by the building façades irregularities, in such a way that two similar streets (in size) can produce two different sound fields for two different building façades. However, most of the existing softwares and models take only the specular reflection into account implying a significant uncertainty in the sound prediction. The main purpose of this paper is, first, to investigate how the sound field and urban soundscape perception are influenced by building façades, and secondly, to characterize several urban façade by typical reflection laws. Then, a coupling morphological and acoustical database will be built up and introduced in an urban acoustics simulation software, in order to be used by town planners and architects in urban projects. This paper is a part of the national land transport research and innovation program (PREDIT) and is supported by the French ministry for ecology and sustainable development.

Conférence du 15 au 19 mai 2006. Communication par affiche.