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Molecular dynamics simulation of hydrocalumite as adsorbent for anionic radionuclides
No full textInternational audienceHydrocalumite, is a hydration product of aluminum-rich cements, and is known in cement chemistry as an AFm phase. Structurally, it belongs to the family of layered double hydroxides, or “anionic clays”, where positively charged crystal layers require the presence of negatively charged ions in the interlayer space. Therefore, AFm phases can serve as potential adsorbents for anionic radionuclides (e.g., 35Cl−, 125I−, 129I−, 131I−) from aqueous solutions. Here we use classical molecular dynamic simulations to analyze the structure and properties of AFm phases containing Cl− and I−. The classical ClayFF force field is used to quantitatively study the structure, energetics and mobility of anions and H2O molecules in the interlayers of these phases and at their interfaces with CsCl and CsI aqueous solutions. In this study we report that the basal (001) surfaces of AFm phases can strongly adsorb hydrated Cl− and I− anions due to the donated hydrogen bonds from the interfacial hydroxyls, but primarily due to their strong attraction to the structural Ca cations exposed at the surface. However, our simulations show that the adsorption of I− is weaker than that of Cl−, leading to the higher surface mobility of I− due to its stronger chaotropic effect. The interlayer diffusional mobility of the Cl− and I− anions in the AFm phases is also investigated by using the Eyring-Vineyard approach and is shown to be significantly lower than in larger nanopores. Hence, the most likely transport of such anionic radionuclides takes place through the nano- and micro-pores of hardened cement
Characterization of a radiation detector based on opaque water-based liquid scintillator
No full textInternational audienceWe present the characterization of a novel radiation detector based on an opaque water-based liquid scintillator. Opaque scintillators, also known as LiquidO, are made to be highly scattering, such that the scintillation light is effectively confined, and read out through wavelength-shifting fibers. The 1-liter, 32-channel prototype demonstrates the capability for both spectroscopy and topological reconstruction of point-like events. The design, construction, and evaluation of the detector are described, including modeling of the scintillation liquid optical properties and the detector's response to gamma rays of several energies. A mean position reconstruction error of 4.4 mm for 1.6 MeV-equivalent events and 7.4 mm for 0.8 MeV-equivalent events is demonstrated using a simple reconstruction approach analogous to center-of-mass
Offline tagging of radon-induced backgrounds in XENON1T and applicability to other liquid xenon detectors
No full textInternational audienceThis paper details the first application of a software tagging algorithm to reduce radon-induced backgrounds in liquid noble element time projection chambers, such as XENON1T and XENONnT. The convection velocity field in XENON1T was mapped out using and events, and the root-mean-square convection speed was measured to be cm/s. Given this velocity field, background events can be tagged when they are followed by and decays, or preceded by decays. This was achieved by propagating a point cloud as directed by the velocity field, and searching for and decays or decays within a volume defined by the point cloud. In XENON1T, this tagging system achieved a background reduction of with an exposure loss of . The tagging algorithm was also used to produce a population of tagged events with a large enhancement in the fraction. We show that the performance can be improved in XENONnT, and that the performance of such a software-tagging approach can be expected to be further improved in a diffusion-limited scenario. Finally, a similar method might be useful to tag the cosmogenic background, which is relevant to the search for neutrinoless double-beta decay
Colloidal ferrogels for the decontamination of limited access metallic surfaces
No full textInternational audienceHandling nuclear metallic waste is a crucial issue for the nuclear industry, notably by using adapted decontamination processes. Colloidal gels can applied by spraying for the nuclear decontamination of large and plane metallic surfaces, such as walls or floors. However, this implementation mode limits their use for the decontamination of inaccessible or complex geometries surfaces. For that purpose, decontamination ferrogels have been formulated by incorporating magnetite particles in a pre-synthesized colloidal gel able to decontaminate stainless steel. Such gels can thus be attracted by a magnet, allowing its remote application on limited access surfaces. The presence of magnetite particles do not influence the inherent decontamination properties of the gel, but plays a significant role on the spreading properties by increasing the gel viscosity. Then, a linear relationship between the gel thickness and the decontamination possibilities has been highlighted. Furthermore, as the magnetite particles dissolve in the gel with time, spreading properties, and consequently the decontamination properties, are modified. Finally, a formulation compromise has to be found for a long time storage of product while maintaining its efficiency
Light-flavor particle production in high-multiplicity pp collisions at TeV as a function of transverse spherocity
No full textInternational audienceResults on the transverse spherocity dependence of light-flavor particle production (, K, p, , , , , ) at midrapidity in high-multiplicity pp collisions at TeV were obtained with the ALICE apparatus. The transverse spherocity estimator () categorizes events by their azimuthal topology. Utilizing narrow selections on , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The estimator is found to effectively constrain the hardness of the events when the midrapidity () estimator is used. The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced. The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of
Production of doubly charmed hadron and in relativistic heavy ion collisions
No full textInternational audienceHeavy ion collisions provide a unique opportunity for studying the properties of exotic hadrons with two charm quarks. The production of is significantly enhanced in nuclear collisions compared to proton-proton collisions due to the creation of multiple charm pairs. In this study, we employ the Langevin equation in combination with the Instantaneous Coalescence Model (LICM) to investigate the production of and which consists of two charm quarks. We consider as molecular states composed of and mesons. The Langevin equation is used to calculate the energy loss of charm quarks and mesons in the hot medium. The hadronization process, where charm quarks transform into each state as constituents of production, is described using the coalescence model. The coalescence probability between and is determined by the Wigner function, which encodes the information of the wave function. Our results show that the production varies by approximately one order of magnitude when different widths in the Wigner function, representing distinct binding energies of , are considered. This variation offers valuable insights into the nature of through the analysis of its wave function. The is treated as a hadronic state produced at the hadronization of the deconfined matter. Its production is also calculated as a comparison with the molecular state
SUBA-Jet: a new Model for Jets in Heavy Ion Collisions
No full textInternational audienceWe present a new model for jet quenching in a quark gluon plasma (QGP). The jet energy loss has two steps. The initial jet parton with a high virtuality loses energy by a perturbative vacuum parton shower modified by medium interactions until it becomes on shell. Subsequent energy loss originates from elastic and radiative collisions with the medium constituents. Coherency of the radiative collisions is achieved by starting with virtual gluons that act as field dressing of the initial jet parton. These are formed according to a Gunion-Bertsch seed. The QCD version of the LPM effect is obtained by increasing the phase of the virtual gluons through elastic scatterings with the medium. Above a phase threshold, the virtual gluons will be formed and can produce coherent radiation themselves. The model has been implemented in a Monte Carlo code and is validated by successfully reproducing the BDMPS-Z prediction for the energy spectrum of radiated gluons in a static medium. Results for the more realistic case, in which the assumptions of the BDMPS-Z approach are released, are also shown. We investigate the influence of various parameters on the energy spectrum and the transverse momentum distribution, such as the in-medium quark masses, the energy transfer in the recoil process, and the phase accumulation criteria, especially for low and intermediate energy gluons
Microbially formed Mn(IV) oxide as a novel adsorbent for removal of Radium
No full textInternational audienceRadioactivity of Ra isotopes in natural waters is of serious concern. Control of 226Ra concentrations in tailings ponds, which store waste from U ore extraction processes, is an important issue in mill tailings management. In this study, we tested microbially formed Mn(IV) oxide as an adsorbent for removal of Ra in water treatment. Biogenic Mn(IV) oxide (BMO) was prepared using a Mn(II)-oxidizing fungus, Coprinopsis urticicola strain Mn-2. First, adsorption experiments of Sr and Ba, as surrogates for Ra, onto BMO were conducted in aqueous NaCl solution at pH 7. Distribution coefficients for Ba and Sr were estimated to be ∼106.5 and ∼104.3 mL/g, respectively. EXAFS analysis indicated that both Sr and Ba adsorbed in inner-sphere complexes on BMO, suggesting that Ra would adsorb in a similar way. From these findings, we expected that BMO would work effectively in removal of Ra from water. Then, BMO was applied to remove Ra from mine water collected from a U mill tailings pond. Just 7.6 mg of BMO removed >98% of the 226Ra from 3 L of mine water, corresponding to a distribution coefficient of 107.4 mL/g for Ra at pH ∼7. The obtained value was convincingly high for practical application of BMO in water treatment. At the same time, the high distribution coefficient indicates that Mn(IV) oxide can be an important carrier and host phase of Ra in the environment
Comparing fracture openings in mortar using different imaging techniques
No full textInternational audienceAbstract This paper presents a quantitative characterisation of the fracture openings obtained in triaxial shear tests on several cement mortar samples. The comparison was carried out on three samples with various apertures using different methods of semi-destructive and non-destructive characterisation: optical microscopy, scanning electron microscopy, X-ray computed tomography, digital volume correlation and the 14C-polymethylmethacrylate method. The fracture aperture distribution results are in good agreement between the different methods. Although the opening results obtained are comparable, the most advantageous method was considered to be XRCT profile analysis based on the size of the target area studied and the specific characteristics of each technique.</jats:p
ALICE luminosity determination for PbPb collisions at TeV
No full textInternational audienceLuminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb–Pb collisions at a centre-of-mass energy per nucleon pair of √s = 5.02 TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan.This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb–Pb collisions at √s = 5.02 TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be 7.67 ± 0.25 b, in agreement with predictions using the Glauber model