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This study investigates the use of atomic layer deposition (ALD) to mitigate multipacting phenomena inside superconducting radio frequency cavities used in particle accelerators while preserving high quality factors in the 1010 range. The unique ALD capability to control the film thickness down to the atomic level on arbitrary complex shape objects enables the fine-tuning of TiN film resistivity and total electron emission yield (TEEY) from coupons to devices. This level of control allows us to adequately choose a TiN film thickness that provides both high resistivity to prevent Ohmic losses and a low TEEY to mitigate multipacting for the application of interest. The methodology presented in this work can be scaled to other domains and devices subject to RF fields in vacuum and sensitive to multipacting or electron discharge processes with their own requirements in resistivities and TEEY values. [ABSTRACT FROM AUTHOR]

The so-called CALPHAD method is widely used in metallurgy to predict phase diagrams of multi-component systems. The application of the method to oxide systems is much more recent, mainly because of the difficulty of modelling the ionic liquid phase. Since the 1980s, several models have been proposed by various communities. Thermodynamic databases for oxides are available and still under development. The purpose of this article is to discuss the distinct approaches of the method for the calculation of multi-component systems for Portland cement elaboration. The article gives a state of the art of the most recent experimental data and the various calculations for the CaO-Al2O3-SiO2 phase diagram. A literature review of the three binary sub-systems leads to main conclusions: (i) discrepancies are found in the literature for the selected experimental data, (ii) the phase diagram data in the reference books are not complete and up to date and (iii) the two-sublattices model and the modified quasichemical model can be equally used for the modelling of the aluminates liquid. The predictive feature of the CALPHAD method is illustrated using the CaO-Al2O3-SiO2 system with the two-sublattices model: extrapolated (predicted) and fully-assessed phase diagrams are compared in the clinkering zone of interest. The recent application of the predictive method for the calculations of high-order systems (taking into account Fe2O3, SO3, CaF2, P2O5,...) shows that the databases developed with the two-sublattices model and the modified quasichemical model are no longer equivalent. [ABSTRACT FROM AUTHOR]

The effect of grain size on the dielectric properties of Ba0.6Sr0.4TiO3 (BST) ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Fine grained ceramics are obtained by hot uniaxial pressing (HUP). Additionally, the present study is focused on the effect of the nature of milling balls on loss tangent and permittivity. For that, three kinds of balls are tested: calcia, yttria or ceria stabilised zirconia balls. The properties of these samples are evaluated in the range of MHz. The balls induce an involuntary doping of powders which modifies the dielectric properties, especially the Curie temperature and loss tangent. [Copyright &y& Elsevier]

The structural damages caused to some layered hydrated minerals by 2.5 MeV electron irradiation using the SIRIUS platform were studied by powder X-Ray diffraction and, in some cases, by 1H MAS-NMR spectroscopy. It is clearly demonstrated that the radiation damages are distinguishable from the heating effects. It is shown that: i) in all cases electron irradiation leads to distortions of the unit cell and very limited volume expansion, compared to heating; ii) radiation damages increase with increasing the structural complexity of the mineral; iii) portlandite Ca(OH) 2 and brucite Mg(OH) 2 remain crystalline up to high doses (a few GGy), with appearance of stacking fault disorder especially in brucite; iv) brushite CaHPO 4.2H 2 O and gypsum CaSO 4.2H 2 O undergo a phase transformation of type amorphization for brushite involving the strongest intralayer H bond between the acidic proton and the phosphate tetrahedral, and decomposition for gypsum involving interlayer H bonds between water molecules. Investigation of electron irradiation effects at low flux and high dose on structural damage of some layered hydrated minerals (portlandite and brucite, gypsum and brushite). [Display omitted] • X-Ray diffraction study of lamellar hydrated minerals following electron irradiation. • For all compounds, radiation damages cannot be assimilated to heating effects. • Very limited unit cell thermal expansion under irradiation compared to heating. • Gypsum transforms into less hydrated crystalline phases while brushite amorphizes. • Amorphization occurs via the strong intralayer H-bonds linking PO 4 units of brushite. [ABSTRACT FROM AUTHOR]

Abstract: The existence of the previously reported intermetallic phases NiW and NiW2 is refuted on the basis of new experiments involving arc-melted samples. A careful study of the literature shows that these two phases were previously evidenced only in sintered alloys and in diffusion couples, both techniques being very prone to surface contamination. It is shown that the phase previously reported as NiW is in fact the low carbon containing ternary carbide Ni6W6C. The second phase NiW2 is most probably the higher ternary carbide Ni2W4C. This study raises also the question of the existence of the equiatomic phase appearing in the Fe–W phase diagram. A crystal structure Rietveld refinement of the intermediate phase Ni4W is also given in the present work, evidencing large substitutional disorder. [Copyright &y& Elsevier]

Abstract: Bismuth oxide in its δ-phase (high-temperature fluorite structure) is a well-known solid electrolyte owing to its high oxygen ion conductivity. In this work, δ-Bi2O3 thin film was stabilized at room temperature by electrodeposition on different conductor substrates. Electrodeposited thin films have a good quality with an excellent adhesion to the substrate. The crystalline structure and the stability of the deposit were studied by X-ray diffraction (XRD). Both XRD measurements and transmission electron microscopy (TEM) investigation revealed the nanocrystallinity of the films. XRD measurements showed a decrease of nanocrystallites size after thin film annealing. The resistivity measurements showed an excellent conductivity of electrodeposited δ-Bi2O3 thin films with an ionic conductive behaviour and an electrical conductivity value close to the theoretical value: the thin film deposited on a gilded silver substrate exhibit a conductivity of 0.39 S/cm at 440 °C. [Copyright &y& Elsevier]

Thermal conductivity and emissivity measurements on different types of uranium carbide are presented, in the context of the ActiLab Work Package in ENSAR, a project within the 7th Framework Program of the European Commission. Two specific techniques were used to carry out the measurements, both taking place in a laboratory dedicated to the research and development of materials for the SPES (Selective Production of Exotic Species) target. In the case of thermal conductivity, estimation of the dependence of this property on temperature was obtained using the inverse parameter estimation method, taking as a reference temperature and emissivity measurements. Emissivity at different temperatures was obtained for several types of uranium carbide using a dual frequency infrared pyrometer. Differences between the analyzed materials are discussed according to their compositional and microstructural properties. The obtainment of this type of information can help to carefully design materials to be capable of working under extreme conditions in next-generation ISOL (Isotope Separation On-Line) facilities for the generation of radioactive ion beams. [ABSTRACT FROM AUTHOR]

The β decay of 82Ge was re-investigated using the newly commissioned tape station BEDO at the electron-driven ISOL (isotope separation on line) facility ALTO operated by the Institut de Physique Nucléaire, Orsay. The original motivation of this work was focused on the sudden occurrence in the light N=49 odd-odd isotonic chain of a large number of J≤1 states (positive or negative parity) in 80Ga by providing a reliable intermediate example, viz., 82As. The extension of the 82As level scheme towards higher energies from the present work has revealed three potential 1+ states above the already known one at 1092 keV. In addition our data allow ruling out the hypothesis that the 843 keV level could be a 1+ state. A detailed analysis of the level scheme using both an empirical core-particle coupling model and a fully microscopic treatment within a Skyrme-QRPA (quasiparticle random-phase approximation) approach using the finite-rank separable approximation was performed. From this analysis two conclusions can be drawn: (i) the presence of a large number of low-lying low-spin negative parity states is due to intruder states stemming from above the N=50 shell closure, and (ii) the sudden increase, from 82As to 80Ga, of the number of low-lying 1+ states and the corresponding Gamow-Teller fragmentation are naturally reproduced by the inclusion of tensor correlations and couplings to 2p-2h excitations. [ABSTRACT FROM AUTHOR]

Abstract: In the context of radioactive ion beams, fission targets, often based on uranium compounds, have been used for more than 50years at isotope separator on line facilities. The development of several projects of second generation facilities aiming at intensities two or three orders of magnitude higher than today puts an emphasis on the properties of the uranium fission targets. A study, driven by Institut de Physique Nucléaire d’Orsay (IPNO), has been started within the SPIRAL2 project to try and fully understand the behavior of these targets. In this paper, we have focused on five uranium carbide based targets. We present an off-line method to characterize their fission product release and the results are examined in conjunction with physical characteristics of each material such as the microstructure, the porosity and the chemical composition. [Copyright &y& Elsevier]