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Simulations and background estimates for the DAMIC-M experiment
No full textInternational audienceDAMIC-M (Dark Matter in CCDs at Modane) is a near-future experiment aiming to search forlow-mass dark matter particles through their interactions with silicon atoms in the bulk of charge-coupled devices (CCDs). This technique was pioneered by the DAMIC experiment at SNOLAB.Its successor DAMIC-M will have a 25 times larger detector mass and will employ a novel CCDtechnology (skipper amplifiers) which allows to achieve a readout noise of 0.07 electrons. Withthese novelties, DAMIC-M will reach unprecedented sensitivities to dark matter candidates of theso-called hidden sector. A challenging requirement is the control of the radiogenic backgroundat the level of a fraction of events per keV per kg-day of target exposure. Accurate Geant4simulations are being employed to optimise the detector design and drive the material selectionand handling. This proceedings provides a comprehensive overview of the explored detectordesigns, the estimated background, and the strategies for its mitigation
Production of scandium radionuclides for theranostic applications: towards standardization of quality requirements
No full textInternational audienceAbstractIn the frame of “precision medicine”, the scandium radionuclides have recently received considerable interest, providing personalised adjustment of radiation characteristics to optimize the efficiency of medical care or therapeutic benefit for particular groups of patients. Radionuclides of scandium, namely scandium-43 and scandium-44 (43/44Sc) as positron emitters and scandium-47 (47Sc), beta-radiation emitter, seem to fit ideally into the concept of theranostic pair. This paper aims to review the work on scandium isotopes production, coordination chemistry, radiolabeling, preclinical studies and the very first clinical studies. Finally, standardized procedures for scandium-based radiopharmaceuticals have been proposed as a basis to pave the way for elaboration of the Ph.Eur. monographs for perspective scandium radionuclides.</jats:p
Neutrino Physics with an Opaque Detector
No full textInternational audienceIn 1956 Reines & Cowan discovered the neutrino using a liquid scintillator detector. The neutrinos interacted with the scintillator, producing light that propagated across transparent volumes to surrounding photo-sensors. This approach has remained one of the most widespread and successful neutrino detection technologies used since. This article introduces a concept that breaks with the conventional paradigm of transparency by confining and collecting light near its creation point with an opaque scintillator and a dense array of optical fibres. This technique, called LiquidO, can provide high-resolution imaging to enable efficient identification of individual particles event-by-event. A natural affinity for adding dopants at high concentrations is provided by the use of an opaque medium. With these and other capabilities, the potential of our detector concept to unlock opportunities in neutrino physics is presented here, alongside the results of the first experimental validation
Soft-Dielectron Excess in Proton-Proton Collisions at = 13 TeV
No full textInternational audienceA measurement of dielectron production in proton-proton (pp) collisions at TeV, recorded with the ALICE detector at the CERN LHC, is presented in this Letter. The data set was recorded with a reduced magnetic solenoid field. This enables the investigation of a kinematic domain at low dielectron invariant mass and pair transverse momentum that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of , , and event multiplicity . The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured ratio in pp and proton-nucleus (p-A) collisions, assuming that this ratio shows no strong dependence on collision energy at low transverse momentum. Comparison of the measured dielectron yield to the hadronic cocktail at GeV/ and for GeV/ indicates an enhancement of soft dielectrons, reminiscent of the 'anomalous' soft-photon and -dilepton excess in hadron-hadron collisions reported by several experiments under different experimental conditions. The enhancement factor over the hadronic cocktail amounts to in the ALICE acceptance. Acceptance-corrected excess spectra in and are extracted and compared with calculations of dielectron production from hadronic bremsstrahlung and thermal radiation within a hadronic many-body approach
Fusion and fission barrier heights and positions within the Generalized Liquid Drop Model
No full textInternational audienceThe fusion and fission barriers have been determined with a Generalized Liquid Drop Model taking into account the proximity forces acting between surfaces in regard, the charge and mass asymmetry, the shell and pairing effects and quasimolecular shapes. The heights and positions of these barriers have been compared with the empirical results deduced from the experimental data. There is an overall agreement for the fusion barrier heights for most of the reactions. These fusion barrier heights may also be calculated from a proposed analytic formula or other formulas. The empirical fission barrier heights lie always between the values given by the GLDM and neglecting the microscopic effects in the fragments and the values determined in including the deformation and shell and pairing effects of the fragments
Magnetic Anisotropy in a Cubane-like Ni Complex: An Ab Initio Perspective
No full textInternational audienceMagnetic anisotropy, in the absence of an external magnetic field, relates to the degeneracy lift of energy levels. In the standard case of transition metal complexes, this property is usually modeled by an anisotropic spin Hamiltonian and one speaks of “zero-field splitting” (ZFS) of spin states. While the case of mononuclear complexes has been extensively described by means of ab initio quantum mechanical calculations, the literature on polynuclear complexes studied with these methodologies is rather scarce. In this work, advanced multiconfigurational wave function theory methods are applied to compute the ZFS of the ground S = 4 state of an actual tetranickel(II) complex, displaying a magnet behavior below 0.5 K. First, the isotropic couplings are computed in the absence of the spin–orbit coupling operator, in the full complex and also in clusters with only two active nickel(II) centers, confirming the occurrence of weak ferromagnetic couplings in this system. Second, the single-site magnetic anisotropies are computed on a cluster bearing only one active nickel(II) site, showing that the single-site anisotropy axes are not oriented in an optimal fashion for generating a large uniaxial molecular anisotropy. Furthermore, the possibility for involving only a few local orbital excited states in the calculation is assessed, actually opening the way for a consistent and manageable treatment of the ZFS of the ground S = 4 state. Third, multiconfigurational calculations are performed on the full complex, confirming the weak uniaxial anisotropy occurring for this state and also, interestingly, revealing a significant contribution of the lowest-lying orbitally excited S = 3 states. Overall, by comparison with the experiment, the reported results question the common habit of using only one structure, in particular derived from a crystallography experiment, to compute magnetic anisotropy parameters
Effect of bacterial siderophore on cesium dissolution from biotite
No full textInternational audienceIn this study, the adsorption of cesium (Cs) on biotite and dissolution of Cs from Cs-bearing biotite using a siderophore were investigated aiming to contribute to the elucidation of radiocesium migration mechanisms in the soil environment. Thus, a siderophore was extracted and purified from the culture medium of Pseudomonas sp., and the purified siderophore was used in five consecutive dissolution experiments of biotite samples. Prior to the dissolution experiments, Cs was adsorbed on a hardly weathered biotite powder sample. The major components of the biotite (Al, Fe, and Mg) were dissolved almost stoichiometrically, strongly suggesting that the siderophore selectively dissolves the broken edges of the biotite. The amount of the dissolved Cs decreased by increasing the repetition times of the dissolution experiment. Therefore, the Cs adsorbed on the broken edges was dissolved rapidly as the siderophore dissolved the broken edges, and then, the Cs adsorbed on the outer planar surface of the biotite particles was slowly dissolved because the siderophore did not directly dissolve the outer planar surface of the biotite but dissolved the surface edge
Rn emanation measurements for the XENON1T experiment
No full textInternational audienceThe selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a Rn activity concentration of 10\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg} in of xenon. The knowledge of the distribution of the Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the Rn activity concentration in XENON1T. The final Rn activity concentration of (4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg} in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment