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The use of stable lead isotopes for the identification of the sources and transport processes leading to the release of radioactive contaminants downstream of former uranium mine sites
No full textInternational audienceRadioactive enriched materials generated by uranium mining activities potentially release radionuclides and associated heavy metals into the environment, leading to high uranium accumulation in soils and sediments around the former uranium mine. However, high uranium content comparable to that from mining activities, due to natural weathering and erosion of local bedrock was reported (up to 6000 mg.kg-1). Thus, highlighting the potential sources and mechanisms driving radioactive elements dissemination in the vicinity of former U mines is a key element for the decision-making process, effective management, and remediation of contaminated sediments and soils. This research aims to identify the sources of radioactive contaminants and their transport mechanism using stable Pb isotopes and radioactive disequilibrium of the 238U-decay series. The study area is a wetland located downstream of the former Rophin U mine (Zone atelier territoires uranifères, France). Soils and sediments were sampled in the wetland and radiological and chemical analyses were performed (platforms PATERSON and LUTECE, IRSN). The uranium content here reaches 16000 mg.kg-1 in the surface organic layer (34 mg.kg-1 in local bedrock). The radiogenic 206Pb/207Pb ratio (~1.73) and the alignments of samples in the three Pb isotopes (206Pb, 207Pb, 208Pb) plot point out the impact of mining activities. Uranium originates probably from three sources related to the mining history of the site: i) pitchblende UO2 due to mechanical and chemical processing from Bois Noirs ore ii) parsonsite Pb2(UO2)(PO4)2, the local dominant U mineralization and iii) U from the local geochemical background. The high content of common Pb in parsonsite hides its radiogenic Pb signature limiting thus the use of the Pb isotopes as a relevant fingerprint for this case. Additionally, observations of Pb-bearing phases associated with phosphate by SEM strengthen our hypothesis. The variation of activity ratio 230Th/238U measured by gamma spectrometry also indicates the mobility of uranium in the profile, probably due to the fluctuation of the water table in the wetland. Finally, a geostatistical approach was explored to highlight lateral radioelement mobility at the wetland scale based on the data of in situ and mobile gamma measurements. Preliminary findings will be shown during the presentation
Latest development of α emitter imaging and quantification on a large Field Of View for TAT applications
No full textInternational audienceOne of the most important challenges in the production and distribution of α-radionuclides remains the identification and characterization of individual radionuclides in radionuclide chains such as Ac-225. Indeed, due to the nature of alpha emitters which have a strong action at very short range, it is essential to control finely in space and time their bio-distribution.However, at present, the characterization of the nature and spatial distribution of radionuclides in a sample remains long and tedious. Indeed, it necessarily requires the use of two distinct analytical techniques and detectors of different nature. Moreover, the resolutions of the two methods are often different from each other because they also depend on the nature of the detector used, which makes the integration and joint interpretation of these two types of measurements difficult.To overcome these limitations and to simplify and accelerate the measurement process, it is now possible to use a digital autoradiograph capable of combining the measurement of the spatial distribution with the ability to separate and quantify each radionuclide.To do this, a set of temporal and energy spectrometry techniques had to be specifically developed. On the one hand, the use of instruments capable of recording the location of each decay product makes it possible to measure the evolution of the activity of the sample and thus to deduce the contributions of several radionuclides. On the other hand, the development of an innovative method of autoradiographic spectroscopy in particle energy also allows to separate them by measuring their initial energy. Even if the efficiency of the energy spectrum reconstruction is low (4.4%) compared to the efficiency of a simple autoradiography (50%), this new measurement approach offers the possibility to select areas on an autoradiography to perform an energy spectrum analysis in that area
Magnetism in Binuclear Compounds: Theoretical Insights
No full textInternational audienceThis chapter is devoted to theoretical calculations aimed at determining the electronic structure of binuclear complexes, including isotropic and anisotropic interactions in both the strong and in the weak-exchange coupling limits. The theory of effective Hamiltonians is used to extract magnetic anisotropy terms in various regimes and in particular those for which the giant-spin approximation holds. While only a second-rank symmetric tensor is necessary to describe the zero-field splitting in centrosymmetric compounds with a single electron on each metal ion, a 4-rank tensor must also be introduced to describe the anisotropic exchange in the case of two unpaired electrons per metal ion. The magnitude of these additional interactions was found to be larger than those of the well admitted 2-rank tensor. Even though, the magnetic anisotropy of binuclear complexes can often be predicted from the knowledge of the local anisotropy of its mononuclear constituents, the large magnitude of the 4-rank tensor makes theoretical calculations important if not mandatory to rationalize experimental results on firm grounds in systems where anisotropic binuclear interactions are important
Measurement of the angle between jet axes in PbPb collisions at TeV
No full textInternational audienceThis letter presents the first measurement of the angle between different jet axes (denoted as ) in PbPb collisions. The measurement is carried out in the 010% most-central events at TeV. Jets are assembled by clustering charged particles at midrapidity using the anti- algorithm with resolution parameters and and transverse momenta in the intervals GeV/ and GeV/, respectively. Measurements at these low transverse momenta enhance the sensitivity to quarkgluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP shows that the observed narrowing of the PbPb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements discard intra-jet broadening as described in a model calculation with the BDMPS formalism as the main mechanism of energy loss in the QGP. The data are sensitive to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss
Study of the ppK and ppK dynamics using the femtoscopy technique
No full textInternational audienceThe interactions of kaons (K) and antikaons () with few nucleons (N) were studied so far using kaonic atom data and measurements of kaon production and interaction yields in nuclei. Some details of the three-body KNN and NN dynamics are still not well understood, mainly due to the overlap with multi-nucleon interactions in nuclei. An alternative method to probe the dynamics of three-body systems with kaons is to study the final state interaction within triplet of particles emitted in pp collisions at the Large Hadron Collider, which are free from effects due to the presence of bound nucleons. This Letter reports the first femtoscopic study of ppK and ppK correlations measured in high-multiplicity pp collisions at = 13 TeV by the ALICE Collaboration. The analysis shows that the measured ppK and ppK correlation functions can be interpreted in terms of pairwise interactions in the triplets, indicating that the dynamics of such systems is dominated by the two-body interactions without significant contributions from three-body effects or bound states
Probing invisible neutrino decay with KM3NeT-ORCA
No full textInternational audienceIn the era of precision measurements of the neutrino oscillation parameters, upcoming neutrino experiments will also be sensitive to physics beyond the Standard Model. KM3NeT/ORCA is a neutrino detector optimised for measuring atmospheric neutrinos from a few GeV to around 100 GeV. In this paper, the sensitivity of the KM3NeT/ORCA detector to neutrino decay has been explored. A three-flavour neutrino oscillation scenario, where the third neutrino mass state decays into an invisible state, e.g. a sterile neutrino, is considered. We find that KM3NeT/ORCA would be sensitive to invisible neutrino decays with ~ at confidence level, assuming true normal ordering. Finally, the impact of neutrino decay on the precision of KM3NeT/ORCA measurements for , and mass ordering have been studied. No significant effect of neutrino decay on the sensitivity to these measurements has been found
Recent developments & contribution to TAT of systems dedicated to α autoradiography
No full textInternational audienceOne of the main difficulties in the development of TAT remains the difficulty of identifying and localizing the distribution of radiopharmaceuticals in the human body since the decay chain of the associated alpha emitter is generally composed of beta and alpha emitters which makes them difficult to localize accurately by techniques using gamma detection of the decays.To address the need to understand and quantify the spatial distribution of alpha emitting radiopharmaceuticals in tissues at high spatial resolution, important developments or improvements have been made in autoradiography systems. Indeed, as the first molecular imaging technique used for the localization of radiolabeled compounds in biological specimens, autoradiography remains the only technique that allows the imaging of charged particles with an unequalled spatial accuracy. In addition, the new generation of real-time counting imagers allow researchers to optimize acquisition time, have a very high sensitivity allowing the detection of short half-life radionuclides, offer the possibility to image in real time and quantify radioactive concentrations over a wide dynamic range. Moreover, their specific detection process allows the discrimination of several radionuclides in the same experiment and sometimes determine the equilibrium state of the radioactive chains. Nevertheless, as there are many types and configurations of detectors with various compromises in terms of activity quantification, spatial resolution, energy resolution and detection area, it remains complicated to be able to understand the different systems and their respective possibilities of evolution. This work therefore proposes to present the current and future applications of autoradiography and their associated detection systems
Decay Data Uncertainty Propagation in Decay Heat Calculations: A Monte Carlo Approach
No full textInternational audienceA proper characterization of decay heat is essential for nuclear power safety at all stages of thefuel cycle, including reactor operation, spent fuel handling, transportation, reprocessing, anddisposal. This work is based on a Monte Carlo approach to quantify the uncertainty propagationof decay data on decay heat calculations using an in-house code named COCODRILO, which iscoupled with Serpent2. The calculations are performed for thermal fission pulses of 239 Pu and 235 U using ENDF/B-VII.1 and ENDF-VIII.0 nuclear decay data libraries. Results are also comparedwith experimental values at different cooling times. The associated analysis shows the impact ofdecay data uncertainties on decay heat. Moreover, the study underscores the discrepancies indecay heat uncertainty calculation due to decay data without uncertainty information
Interaction des radioéléments (Ra, U) avec les diatomées
No full textDiatoms are ubiquitous unicellular microalgae that are commonly used as bioindicators to evaluate the impact of contaminations on the ecological health of aquatic ecosystems. In recent decades, diatoms have received increasing attention as a decontamination material for removing heavy metals from contaminated effluents or for in situ bioremediation purposes. However, the interactions between diatoms and radioelements, e.g., uranium (U) and radium (Ra), remain relatively unclear and poorly documented. Therefore, this work aims to study, at both the macroscopic and molecular level, the interaction of U and Ra with a xenic Achnanthidium saprophilum diatom culture in which a naturally occurring bacterial community is symbiotically associated to diatoms. Batch-type U and Ra bio-association experiments are performed to evaluate the adsorbed and incorporated fractions of U/Ra in the diatom culture. Besides, various microscopic and spectroscopic techniques are applied to investigate the localization and speciation of U at the cellular level. Results demonstrate the significant bioassociation of U and Ra with the diatoms and highlight the important role of carboxylic and phosphate groups in the U-diatoms interaction. Both adsorption and incorporation are observed for U and Ra in the diatom culture, with their distribution depending on the diatom growth phase and on the contact time. This work contributes to a better understanding of the interaction of U and Ra with the xenic diatom culture and also highlights the contribution of the bacteria symbiotically associated with the diatoms to the overall interactions.Les diatomées sont des microalgues unicellulaires omniprésentes sur Terre et utilisées comme bioindicateurs pour évaluer l'impact de contaminations sur les écosystèmes aquatiques. Elles font également l'objet d'une attention croissante en tant que matériel de décontamination de métaux lourds d’effluents contaminés ou à des fins de biorestauration in situ. Cependant, les interactions entre les diatomées et les radioéléments, notamment l'uranium (U) et le radium (Ra), restent peu documentées. Ce travail vise à étudier tant au niveau macroscopique que moléculaire, les interactions de U et du Ra avec une culture xénique de diatomées Achnanthidium saprophilum, dans laquelle une communauté bactérienne est naturellement associée de manière symbiotique. Des expériences de bio-association de U et du Ra sont faites en présence de diatomées afin d’évaluer les fractions en U/Ra adsorbées et incorporées. En parallèle, diverses techniques de microscopie et de spectroscopie sont appliquées pour étudier la localisation et la spéciation de U au niveau cellulaire. Les résultats démontrent une bio-association significative de U et du Ra avec les diatomées et soulignent le rôle important des groupes carboxyliques et phosphates dans l'interaction U-diatomées. Les deux mécanismes d’adsorption et d’incorporation ont pu être mis en évidence pour U et Ra, la répartition entre les fractions adsorbées et incorporées dépendant de la phase de croissance des diatomées et du temps de contact entre les micro-algues est les radioéléments. Ce travail met également en évidence la contribution significative des bactéries symbiotiquement associées aux diatomées aux interactions globales
