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Cellulose, proteins, starch and simple carbohydrates molecules control the hydrogen exchange capacity of bio-indicators and foodstuffs
No full textInternational audienceOver the past several years, it has become increasingly acknowledged that Organically Bound Tritium (OBT) is the most pertinent tritium form for understanding its behavior and distribution within the biosphere. The fate of tritium actually depends on the accessibility and exchangeability of hydrogen atoms for isotopic exchanges in natural organic matter, especially in widespread biomass biomolecules like carbohydrates or proteins. The present work is therefore aimed at providing a means for improving the knowledge of tritium speciation and distribution on environmental matrices by evaluating the impact of molecular structure of various carbohydrate molecules on OBT behavior. We are thus proposing to assess the exchange capacities of hydrogen from a gas-solid isotopic exchange methodology in wheat grains, water-milfoil and apple environmental matrices using starch, cellulose/proteins and simple carbohydrates as their respective main constituents. For wheat grains, a good agreement was obtained between experimental and theoretical values as a result of the predominantly simple molecular structure of starch. For both water-milfoil and apple, the disparities between experimental and theoretical values showed the occurrence of the buried form of tritium, correlated with the 3D molecular complexity of their main constituents. The key role played by these determinant constituents on hydrogen exchange capacity could thus be experimentally demonstrated on several environmental matrices. These distinct hydrogen exchange capacities were then proven to exert an influence on the NE-OBT distribution on environmental matrix constituents, in yielding critical information to better the understanding of tritium distribution and behavior in the environment
Production of pions, kaons, (anti-)protons and mesons in Xe–Xe collisions at = 5.44 TeV
No full textInternational audienceThe first measurement of the production of pions, kaons, (anti-)protons and mesons at midrapidity in Xe–Xe collisions at is presented. Transverse momentum () spectra and -integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the -to-pion ratio with increasing final-state multiplicity
Structure and properties of calcium aluminates and their aqueous interfaces revisited with a new series of ClayFF-based atomistic simulations
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Empowering JUNO physics by means of an ancillary photodetection system
No full textInternational audienceJUNO is a liquid scintillator detector currently under construction in the south of China. JUNO aims to detect the disappearance of reactor antineutrinos at an average baseline of 53 km, with the primary goal of determining the neutrino mass ordering and performing a sub-percent measurement of three of the neutrino oscillation parameters. This physics program is rooted in the detector’s unprecedented capability to detect 1345 photoelectrons (p.e)/MeV of deposited energy, yielding a 3% energy resolution at 1 MeV. The main photodetection system comprises 17,612 20-inch “large” photomultipliers (LPMTs), each of which experiences an illumination varying over two orders of magnitude. To help calibrating the LPMT response in such a demanding environment, JUNO will be instrumented with additional 25,600 custom-made 3" "small" photomultipliers (SPMTs). They will operate in photon-counting regime by detecting at most 1 PE per neutrino interaction, hence providing a complementary energy estimator with a novel dual calorimetry technique. In addition, the SPMT system is designed to provide a semi-independent measurement of the “solar” oscillation parameters, to aid the measurement of supernova neutrinos, to study the proton decay and to improve the muon track reconstruction, whose performance is pivotal for background rejection. Like the LPMTs, the SPMTs together with their power and readout systems, will have to operate under water for over 20 years, posing challenging constraints on the design, reliability and implementation of this major subsystem of JUNO. In this talk, we will present the innovative design of the JUNO SPMT system, its impact on physics, and the current status of SPMT production and testing
Radiation exposure of microorganisms living in radioactive mineral springs
No full textInternational audienceThe TIRAMISU collaboration gathers expertise from biologists, physicists, radiochemists and geologists within the Zone-Atelier Territoires Uranifères (ZATU) in France to analyze the radiation exposure of microorganisms living in naturally radioactive mineral springs. These springs are small waterbodies that are extremely stable over geological time scales and display different physicochemical and radiological parameters compared to their surroundings. Water and sediment samples collected in 27 mineral springs of the volcanic Auvergne region (Massif Central, France) have been studied for their microbial biodiversity and their radionuclide content. Among the microorganisms present, microalgae (diatoms), widely used as environmental indicators of water quality, have shown to display an exceptional abundance of teratogenic forms in the most radioactive springs studied (radon activity up to 3700 Bq/L). The current work presents a first assessment of the dose received by the diatoms inhabiting these ecosystems. According to ERICA tool, microorganisms living in most of the sampled mineral springs were exposed to dose rates above 10 μGy/h due to the large concentration of radium in the sediments (up to 50 Bq/g). Radiological analyses of water and sediments were used as inputs to Monte Carlo simulations at micro-(GATE) and nano- (Geant4-DNA) scale in order to assess the direct and indirect damages on the diatom DNA.</jats:p
femtoscopy in Pb-Pb collisions at = 2.76 TeV
No full textInternational audienceThe first measurements of the scattering parameters of ΛK pairs in all three charge combinations (ΛK+, ΛK−, and ΛKS0) are presented. The results are achieved through a femtoscopic analysis of ΛK correlations in Pb-Pb collisions at sNN=2.76 TeV recorded by ALICE at the Large Hadron Collider. The femtoscopic correlations result from strong final-state interactions and are fit with a parametrization allowing for both the characterization of the pair emission source and the measurement of the scattering parameters for the particle pairs. Extensive studies with the THERMINATOR 2 event generator provide a good description of the nonfemtoscopic background, which results mainly from collective effects, with unprecedented precision. Furthermore, together with HIJING simulations, this model is used to account for contributions from residual correlations induced by feed-down from particle decays. The extracted scattering parameters indicate that the strong force is repulsive in the ΛK+ interaction and attractive in the ΛK− interaction. The data hint that the ΛKS0 interaction is attractive; however, the uncertainty of the result does not permit such a decisive conclusion. The results suggest an effect arising either from different quark-antiquark interactions between the pairs (ss¯ in ΛK+ and uu¯ in ΛK−) or from different net strangeness for each system (S=0 for ΛK+, and S=−2 for ΛK−). Finally, the ΛK systems exhibit source radii larger than expected from extrapolation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle Λ and K source distributions
Diffusion Behavior of Methane in 3D Kerogen Models
No full textInternational audienceAs global energy demand increases, natural gas recovery from source rocks is attracting considerable attention since recent development in shale extraction techniques has made the recovery process economically viable. Kerogens are thought to play an important role in gas recovery; however, the interactions between trapped shale gas and kerogens remain poorly understood due to the complex, heterogeneous microporous structure of kerogens. This study examines the diffusive behavior of methane molecules in kerogen matrices of different types (Type I, II, and II) and maturity levels (A to D for Type II kerogens) on a molecular scale. Models of each kerogen type were developed using simulated annealing. We employed grand canonical Monte Carlo simulations to predict the methane loadings of the kerogen models and then used equilibrium molecular dynamics simulations to compute the mean square displacement of methane molecules within the kerogen matrices under reservoir-relevant conditions, that is, 365 K and 275 bar. Our results show that methane self-diffusivity exhibits some degree of anisotropy in all kerogen types examined here except for Type I-A kerogens, where diffusion is the fastest and isotropic diffusion is observed. Self-diffusivity appears to correlate positively with pore volume for Type II kerogens, where an increase in diffusivity is observed with increasing maturity. Swelling of the kerogen matrix up to a 3% volume change is also observed upon methane adsorption. The findings contribute to a better understanding of hydrocarbon transport mechanisms in shale and may lead to further development of extraction techniques, fracturing fluids, and recovery prediction
Impact of disruption between options of plutonium multi-recycling in PWRs and in SFRs
No full textInternational audienceDuring the recent ten years, the estimation of future uranium demands has changed greatly, and SFR competitiveness is called again into question. In this context, a planning of plutonium multi-recycling in PWRs for the near-term decades has been announced in France, which replaces the objective of future SFR deployment. However, the mid-term policy concerning the future reactor system is always uncertain, and the demand of SFR deployment may re-increase significantly. This study looks into this possibility and analyzes the consequences of such back and forth between different plutonium multi-recycling strategies. The newly developed methodology of robustness assessment is applied to the problem, considering the objective disruptions to take into account the deep uncertainties about nuclear future. Two prior trajectories of plutonium multi-recycling, one involving the use of MIX fuel in PWRs and the other considering the SFR deployment, are analyzed first. The disruption of the strategy using MIX is then supposed under the re-consideration of future SFR deployment. To quantify the impacts of using MIX on deployment timing, we investigate the earliest time for which the fleet substitution with SFRs can be completed. To supplement, the prior strategy of SFR deployment is also disrupted under the context of halting the start of new SFR. The plutonium multi-recycling in PWRs, regarded as adaptive strategy, aims to minimize the idle plutonium. In these robustness assessments, numerous outputs of interests are analyzed, in order to provide a comprehensive evaluation of consequences of prior strategies, regarding the uncertain disruptions and optimal readjustments