UCx_x target design for the SPIRAL 2 project and the ALTO project

ACC NESTERInternational audienceTwo ways of production of radioactive beams using uranium carbide targets are taken into consideration: fission induced by fast neutrons and by bremsstrahlung radiation. For the SPIRAL 2 project, the fission of 238U in uranium carbide target will be induced by a neutron flow created by bombarding a carbon converter with a 40 MeV high intensity deuteron beam. Calculations and design of the target in order to reach 1013 fissions/s with good release time have been done. The second way is the photofission using an electron beam. In 2005 the ALTO project (Accélérateur Linéaire Auprès du Tandem d'Orsay) will give a 50 MeV/10$\mu$A electron beam. This facility will allow more than 1011 fissions/s. In this case, the electron beam hits the target without converter. Calculations realised in order to estimate the production are used to choose the best target shape. For the two cases some R & D on targets to improve release is described

Ion sources at GANIL

International audienceThe GANIL produces since many years heavy ion beams with Electron Cyclotron Resonance ion sources. Different facilities have been constructed during the last years in order to allow experiments in a large range of energy (from some tens of kV to 100 MeV/nucleon). The list of available ions has been greatly extended with the construction of the SPIRAL1 facility that produces and accelerates radioactives ions . An overview of the different developments made at GANIL for stable and radioactive ion beam production including the sources for the SPIRAL2 project is given in this paper

Time projection chambers for the T2K near detectors

The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator-bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker is used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/Nomad dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system

Durcissement superficiel par laser CO

Le durcissement superficiel par faisceau laser CO2 continu n’est généralement pas recommandé dans le cas des pièces métalliques de grandes surfaces par suite de l’important gradient de structure créé par les recouvrements de passes. En effet, les conséquences de ce gradient sur l’hétérogénéité du durcissement et la distribution des contraintes résiduelles peuvent compromettre la tenue en service, et particulièrement la résistance à la fatigue des pièces traitées. La solution industrielle réside dans la recherche et l’optimisation du couple acier/paramètre de traitement laser, permettant de limiter voire d’éviter l’apparition de zones adoucies, sièges de contraintes résiduelles de traction. Les modes d’interaction microstructure-traitement laser orientent les recherches vers les aciers à dispersoïdes susceptibles de compenser, par effet de durcissement structural, l’adoucissement résultant des recouvrements de passes. Dans ce cadre, nous avons étudié l’influence de deux types de traitements laser sur l’évolution des structures métallurgiques, des contraintes résiduelles dans les zones de recouvrement de passes et leurs conséquences sur la tenue en fatigue de l’acier à dispersoïdes de nuance 17MnCuNi7. Il en résulte une profondeur des couches affectées pouvant atteindre 2 mm, avec des modifications structurales étroitement liées aux gradients thermiques spécifiques à chaque type de traitement. Le durcissement maximum est atteint en surface, avec des valeurs voisines de 700 HV0,1 attribuées à une transformation martensitique. La distribution homogène des carbures mixtes de vanadium et de niobium, limite l’adoucissement dans les zones de recouvrement. Les contraintes résiduelles sont de compression dans les zones durcies comme dans les zones adoucies. La tenue en fatigue de l’acier de nuance 17MnCuNi 7 durci par traitement laser dépend en premier lieu du champ de contraintes résiduelles dans les couches affectées par le traitement, en dépit des pertes de dureté provoquées par le recouvrement de passes. Les améliorations apportées par ce traitement, en terme de limite d’endurance, varient de 10 à 20 % par rapport à l’état de référence, trempé revenu

Three-dimensional characterization of fatigue-relevant intermetallic particles in high-strength aluminium alloys using synchrotron X-ray nanotomography

International audienceSecond-phase particles and small porosities are known to favour fatigue crack initiation in high-strength aluminium alloys 2050-T8 and 7050-T7451. Using high-resolution X-ray tomography (320 nm voxel size), with Paganin reconstruction algorithms, the probability that large clusters of particles contain porosities could be measured for the first time in 3D, as well as precise 3D size distributions. Additional holotomography imaging provided improved spatial resolution (50 nm voxel size), allowing to estimate the probability of finding cracked particles in the as-received material state. The extremely precise 3D shape (including cracks) as well as local chemistry of the particles has been determined. This experiment enabled unprecedented 3D identification of detrimental stress risers relevant for fatigue in as-received aluminium alloys

Optimization of isol UCx_x targets for fission induced by fast neutrons or electrons

ACC NESTE

Optimization of isol UCx_x targets for fission induced by fast neutrons or electrons

ACC NESTE

Fabrication of ultra-low radioactivity detector holders for Edelweiss-II

International audienceIn its first stage, the EDELWEISS-II dark matter experiment will use 21×320 g ionization-heat bolometers with NTD thermal sensors. To improve the present sensitivity of EDELWEISS to WIMP interactions by a further factor 100, ultra-low radioactivity detector holders exclusively made of copper and Teflon have been designed. The new design is using the relative expansion coefficients of copper, Teflon and germanium to hopefully ensure a dissipation-free detector holding. In order to validate this new holder, we need to compare the vibration behavior of the old holder and the new one. The amplitude of the bolometer vibrations is measured using the variation of capacitance between electrodes sputtered on the Ge crystal and reference electrodes fixed above the detector holders. We present noise measurements and compare them to the equivalent measurements using the detector holders of the Edelweiss-I experiment, which gave very satisfying results

Optimization of isol UCx_x targets for fission induced by fast neutrons or electrons

ACC NESTE