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Nouveaux développements pour la détermination du radium dans des solutions synthétiques et des eaux naturelles
No full textRadium is a highly radiotoxic natural radioelement. It is, therefore, important to analyze it in a radiological monitoring context, with the need to develop concentration/separation methods. Under this context, this work fits with two challenges: (i) testing a new specific resin for Ra , (ii) the realization of Ra concentration/separation step via the technique of “Diffusive Gradients in Thin films” (DGT). In the first part of the thesis, the performances of the new resin (selectivity, efficiency) were compared with some commercial resins. The AnaLig® Ra-01 resin shows the best performance while the Chelex®-100 resin is extremely sensitive to salinity. This is also the case for the new Ra specific resin, although its efficiency and selectivity are very high for lightly salted waters. The studies then focused on the DGT technique coupled with HR-ICP-MS analyzes. In the case of AnaLig® Ra-01 and Chelex®-100, the studies were conducted from the laboratory (with synthetic solutions) to the field (in a natural water spring enriched with Ra). The operation of DGT Chelex®-100 samplers was strongly disturbed by the presence of competing elements, while that of DGT AnaLig® Ra-01 samplers appeared to be promising even for in situ deployment. With regard to the new specific resin, considerable work has been done on the preparation of the reactive supports (chelating gels and impregnated discs). In both cases, the results in the laboratory appeared to be poor and more work will have to be done on the preparation phase of these supports before a possible application in the field.Le radium est radioélément naturel hautement radiotoxique. Il est donc important de l’analyser dans un contexte de surveillance, avec la nécessité de développer des méthodes de concentration/séparation. C’est dans ce contexte que s’inscrit ce travail avec deux enjeux (i) le test d’une nouvelle résine spécifique pour le Ra et (ii) la réalisation de l’étape de concentration/séparation dans la nature via la technique « Diffusive Gradients in Thin films » (DGT). Dans une première partie de la thèse, les performances de la nouvelle résine (sélectivité, efficacité) ont été comparées à des résines commerciales. La résine AnaLig® Ra-01 présente les meilleures performances alors que la résine Chelex®-100 est extrêmement sensible à la salinité. C’est le cas également de la nouvelle résine spécifique au Ra, bien que très efficace et sélective dans les eaux peu chargées. Les études se sont ensuite concentrées sur la technique DGT couplée à des analyses par ICP-MS-HR. Pour le cas de l’AnaLig® Ra-01 et la Chelex®-100, les études ont été effectuées du laboratoire (avec des solutions modèles) au terrain (dans une source naturellement riche en Ra). Si le fonctionnement des capteurs DGT Chelex®-100 est fortement perturbé par la présence d’éléments compétiteurs, celui des DGT AnaLig® Ra-01 apparaît comme très prometteur y compris en déploiement in situ. Pour ce qui est de la nouvelle résine spécifique, un travail conséquent a porté sur la préparation des supports réactifs (gels chélatants et disques imprégnés). Dans les deux cas, les résultats au laboratoire sont apparus médiocres et un travail plus conséquent devra être effectué sur la phase de préparation de ces supports avant une éventuelle application sur le terrain
Deciphering the non-linear impact of Al on chemical durability of silicate glass
No full textInternational audienceRole of Al in aluminosilicate glasses remains misunderstood; at low concentration it increases the glass resistance to hydrolysis whereas at high concentration an opposite effect is observed. To understand the origin of the phenomenon at atomic level, we performed 577 MD simulations through potential mean force (PMF) method to estimate the activation barriers and to correlate statistically with their corresponding structural features of silicate and aluminosilicate glasses. PMF simulation results validated by the experimental studies revealed that Al is very easy to dissociate, but increases the resistance of glass towards water through significantly increasing both the strength of Si and network connectivity. In contrast, at high Al concentration, preferential dissolution of Al weakens the silicate network, and so the glass resistance becomes very poor. Activation barrier for dissociating bonds around Al is 0.46eV, which is significantly less than Si in pure silicate (1.22eV) and Si in aluminosilicate glass (1.34eV). Si with Al as second neighbour had significantly higher activation energy than Si in pure silicate glass
Atomistic simulations of ettringite and its aqueous interfaces: Structure and properties revisited with the modified ClayFF force field
No full textInternational audienceEttringite, (Ca6[Al(OH)6]2[SO4]3·nH2O, n = 24–27), is one of the common phases of cement and plays an important role in cement chemistry as the primary cause of sulphate corrosion in Portland cement. Molecular dynamic computer simulations have already been applied earlier to model the crystal structure of ettringite and its interfaces with aqueous salt solutions. A recently developed version of the widely used ClayFF force field allows now to explicitly take into account the bending of M-O-H angles of (M = Al, Ca), leading to a much better agreement of the simulation results with available experimental data. The structure and dynamics of bulk ettringite crystal and its interfaces with NaCl and Na2SO4 aqueous solutions are quantitatively evaluated here for the new modified version of the force field, ClayFF-MOH, and compared with the results obtained with the earlier version, ClayFF-orig. The crystallographic parameters, elastic properties, the structure and dynamics of intracrystalline hydrogen bonding network and the vibrational spectra of ettringite are calculated by classical molecular dynamics simulations and quantitatively compared with available experimental data using both versions of ClayFF. Atomic density profiles for solution species at the ettringite surface, atomic distributions within the crystal-solution interface, and the interfacial diffusional mobility of the species are also calculated and compared. The results clearly demonstrate the importance of the explicit inclusion of M-O-H angular bending terms for accurate modeling of the mineral systems containing structural and interfacial hydroxide groups. The simulation results also show that the application of the new more accurate ClayFF-MOH version of the force field leads to the formation of a stronger hydrogen bonding network structure in the intercolumnar space of the ettringite crystal and at its surface, resulting in a stronger immobilization of the water molecules involved, as well as the ions. The ionic adsorption at the ettringite surface is also generally stronger than it was predicted by the earlier model
Witten index for weak supersymmetric systems: Invariance under deformations
No full textInternational audienceWhen a 4D supersymmetric theory is placed on S3 × ℝ, the supersymmetric algebra is necessarily modified to su(2|1) and we are dealing with a weak supersymmetric system. For such systems, the excited states of the Hamiltonian are not all paired. As a result, the Witten index Tr{(−1)Fe−βH} is no longer an integer number, but a β-dependent function. However, this function stays invariant under deformations of the theory that keep the supersymmetry algebra intact. Based on the Hilbert space analysis, we give a simple general proof of this fact. We then show how this invariance works for two simplest weak supersymmetric quantum mechanical systems involving a real or a complex bosonic degree of freedom
Atomistic Modeling of the Structural and Dynamic Properties of Aqueous NaCl and Na2SO4 Solutions in the Interlayer Space of Ettringite
No full textInternational audienceThe use of a new modification of the ClayFF force field for molecular dynamics modeling of ettringite crystals and interaction of aqueous NaCl and Na2SO4 solutions with their surface shows that the possibility of explicitly taking into account metal-O-H interactions in the system leads to the formation of stronger hydrogen bonds in the crystal structure and on the surface and to greater localization of the atoms of both the crystalline phase and solutions in the subsurface zone. The relative fractions of the inner- and outer-spheric adsorption of Na+, Cl-, and (SO4)(2-) ions and the mobility of H2O molecules in both solutions also change. The calculated crystal lattice parameters and the density of ettringite remained almost unchanged between the old and new versions of the ClayFF force field, but the accuracy of reproduction of the elastic characteristics of the crystal markedly increased
Net-proton number cumulant ratios as a function of beam energy from an expanding nonequilibrium chiral fluid
No full textInternational audienceThe beam energy scan program at RHIC provides data on net-proton number fluctuations with the goal to detect the QCD critical end point and first-order phase transition. Interpreting these experimental signals requires a vital understanding of the interplay of critical phenomena and the nonequilibrium dynamics of the rapidly expanding fireball. We study these aspects with a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via a Langevin equation. Assuming a sigma-proton coupling through an effective proton mass, we relate cumulants of the order parameter and the net-proton number at freeze-out and obtain observable cumulant ratios as a function of beam energy. We emphasize the role of the nonequilibrium first-order phase transition where a mixed phase with gradual freeze-out can significantly alter the cumulants. We find that the presence of a critical end point is clearly visible in the cumulant ratios for a relatively wide range of center-of-mass energies
Heavy-flavour (open and hidden) transport and energy loss: open questions and what to do in 2030+
No full textNational audiencetalk sur les perspective au workshop "saveures lourdes" du GDR QC
What can we learn from earthbound experiments about the equation of state of strongly interacting matter?
No full textInternational audienceWe present results from earthbound experiments on the equation of state of strongly interacting matter, which are relevant for neutron start and gravitational wave studies
Développement d'une cible enrichie de gadolinium pour la mesure de la section efficace et la production future de terbium pour la médecine nucléaire
No full textRadionuclides of terbium have attracted much attention for their potential applications in nuclear medicine. However, the short supply of terbium isotopes has limited their applications. This work proposes to use enriched gadolinium targets to produce terbium radioisotopes in biomedical cyclotrons via light-particle-induced reactions. The Auger and gamma emitter 155Tb is taken as a study case using the reaction 155Gd(d,2n)155Tb. To estimate the production yield, thin Gd- containing targets have been firstly developped to measure the cross sections. To this end, the co-electrodeposition method has been chosen to manufacture Ni-Gd2O3 composite targets. Several process parameters that have an impact on deposit quality are stutied to increase the Gd content (up to 3 mg in the deposit). The cross section measurement of natGd(d,2n)Tb, as a proof-of-conception experiment, has been carried out at GIP ARRONAX cyclotron facility using natural Ni-Gd2O3 targets. The production yield is estimated using these results. Thick targets have also been developped via pelletizing method for mass production. The optimal experimental conditions and pellet properties under these conditions have been investigated. An enriched 155Gd2O3 target was irradiated with an incident energy of 15 MeV. The production yield of 155Tb was found to be 10 MBq/μAh and the purity was 89%, which are consistent with the estimation. The coproduction of other Tb isotopes and the recycle of Gd are also involved in this thesis.Les radionucléides du terbium ont attiré beaucoup d'attention pour leurs applications potentielles en médecine nucléaire. Cependant, leurs applications ont limitées par leur pénurie. Ce travail propose d'utiliser des cibles de gadolinium enrichies pour produire du terbium dans des cyclotrons biomédicaux. Le radionucléide 155Tb est pris comme cas d'étude via la réaction 155Gd(d,2n)155Tb. Pour estimer le rendement de production, des cibles minces contenant du Gd ont été développées pour la mesure des sections efficaces. La méthode de co-électrodéposition a été choisie pour fabriquer des cibles composées Ni-Gd2O3. Plusieurs paramètres ont été étudiés pour augmenter la masse de Gd dans la cible. Les sections efficaces de la réaction 155Gd(d,2n)Tb ont été mesurées au cyclotron du GIP ARRONAX dans une gamme d'énergie de 8 MeV à 30 MeV. Le rendement est estimé à partir de ces nouveaux résultats. Pour la production de masse, des cibles épaisses ont été développées via la méthode de pastillage. La condition expérimentale optimale et les propriétés sous cette condition ont été étudiées. Une cible de Gd2O3 enrichie a été irradiée avec une énergie incidente de 15 MeV. Le rendement est de 10 MBq/μAh et la pureté est de 89 %. La coproduction d'autres isotopes de Tb, et le recyclage de Gd sont également présentés dans cette thèse
Économie de l’énergie nucléaire 2: Enjeux dans la transition énergétique
No full textInternational audienceCet ouvrage expose les éléments économiques factuels, précis, complets et accessibles de l’énergie nucléaire afin de contribuer à un débat éclairé et dépassionné. Il analyse les aspects économiques de la gestion des combustibles usés et notamment les coûts et les modes de financement de l’entreposage de longue durée et du stockage géologique profond. Les coûts économiques d’un accident nucléaire sont aussi traités selon les angles théorique et appliqué à partir de l’accident de Fukushima. Économie de l’énergie nucléaire 2 s’intéresse également aux aspects industriels et politiques du mix énergétique du futur. L’énergie nucléaire est ainsi replacée dans le contexte plus global du marché européen de l’électricité. Enfin, ce livre offre un panorama des scénarios énergétiques à l’échelle de la France, mais également du monde.Coordonnateurs : Jacques Percebois "Professeur émérite à l’Université de Montpellier, Jacques Percebois est le fondateur du CREDEN et d’un master en économie de l’énergie. Auteur de plusieurs ouvrages sur l’énergie, il a été membre de plusieurs commissions nationales sur le nucléaire." Nicolas Thiollière "Nicolas Thiollière est physicien nucléaire, enseignant-chercheur à IMT Atlantique et rattaché au laboratoire de recherche fondamentale Subatech. Il est spécialiste de la modélisation des réacteurs et du cycle du combustible.