[en] The microwave heating of a pulsed Ba photoplasma and its free expansion into a vacuum is studied theoretically and experimentally. The vapor production apparatus and the two step photoionization scheme have been described in a previous paper. The heating experimental device is essentially a microwave loop working in a self tuning oscillator mode composed of a transmission rectangular microwave resonator associated with a TWT power amplifier. The amplifier is coupled to the rectangular resonator by two coaxial-line probes: with a coupling coefficient very close to 1 at the input and with a coefficient equal about 10^-3 at the output

[en] Until the last ten years , the tubes of the Steam Generators of the Nuclear Stations were inspected by means of Eddy Current with analogical checkings-chains. HBS Company has perfected a numerized checking-chain allowing transmission up to 300 m of the E.C. signals. In a near future, it will be then possible to do periodical inspections of Steam Generators from cabins located out of the reactor building

[en] A knowledge of diffusion mechanisms and the values of associated coefficients is essential for controlling changes in heated materials and alloys with time. In contrast to solids, where a large literature is available, little research has been done on diffusion coefficients in liquid metals. This is due to experimental difficulties: compatibility of the liquid with the measurement cell, high vapor pressures, convective processes. A significant improvement was achieved by the use of the shear cell, which puts the elements into contact with each other at the selected working temperature and isolates the different sections at the end of the diffusion time. This method employs radioactive sources, generally as tracers, which need counting after cooling. Each alloy composition requires a test, increasing the number of experiments needed. To eliminate the use of tracers, we propose a method based on the shear cell procedure for putting the liquids into contact, which allows determination of the interdiffusion coefficient in a liquid alloy in a single experiment from the measurement of a mass spectrometer signal. The experimental principle is shown schematically. Iron is in the upper ceramic cell and uranium in the lower. After stabilizing the temperature and adjusting the detected signal of the spectrometer to the mass of iron, the iron and uranium are brought into contact by rotating the upper cell from outside the vacuum chamber. The diffusion experiment consists in recording the decrease over time of the signal received by the spectrometer. During the diffusion period, the upper surface of the iron is enriched in uranium, thereby decreasing the thermodynamic activity of the iron and the detected signal. (authors)

[en] The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes, ${}^{155}$Gd and ${}^{157}$Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8MeV. The complex level schemes of ${}^{156}$Gd and ${}^{158}$Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd (n,$\mathrm{\gamma <!--\; ??\; -->}$) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user.

[en] This article reports the measurement of the ²³⁵U-induced antineutrino spectrum shape by the Stereo experiment. 43 000 antineutrinos have been detected at about 10 m from the highly enriched core of the ILL reactor during 118 full days equivalent at nominal power. The measured inverse beta decay spectrum is unfolded to provide a pure ²³⁵U spectrum in antineutrino energy. A careful study of the unfolding procedure, including a cross-validation by an independent framework, has shown that no major biases are introduced by the method. A significant local distortion is found with respect to predictions around E _ν ≃ 5.3 MeV. A Gaussian fit of this local excess leads to an amplitude of A = 12.1 ± 3.4% (3.5σ). (paper)

[en] The STEREO experiment is a very short baseline reactor antineutrino experiment aiming at testing the hypothesis of light sterile neutrinos as an explanation of the deficit of the observed neutrino interaction rate with respect to the predicted rate, known as the Reactor Antineutrino Anomaly. The detector center is located 10 m away from the compact, highly ²³⁵U enriched core of the research nuclear reactor of the Institut Laue Langevin in Grenoble, France. This paper describes the STEREO site, the detector components and associated shielding designed to suppress the external sources of background which were characterized on site. It reports the performances in terms of detector response and energy reconstruction.

[en] The STEREO experiment is searching for a non-standard oscillation in the propagation of anti-neutrinos produced by the high flux reactor of the Institut Laue-Langevin which could be the sign for the existence of a sterile state of eV mass and the origin of the reactor anti-neutrino anomaly. In this paper, results from 66 days of reactor turned on and 138 days of reactor turned off are reported excluding large amplitude oscillations. A special focus is put on the data analysis and studies of correlated backgrounds. In particular the origin of the correlated background measured in reactor turned off periods is discussed. This background mainly originates from neutrons produced by cosmic radiation. (authors)

[en] The precise modeling of the de-excitation of Gd isotopes is of great interest for experimental studies of neutrinos using Gd-loaded organic liquid scintillators. The FIFRELIN code was recently used within the purposes of the STEREO experiment for the modeling of the Gd de-excitation after neutron capture in order to achieve a good control of the detection efficiency. In this work, we report on the recent additions in the FIFRELIN de-excitation model with the purpose of enhancing further the de-excitation description. Experimental transition intensities from the EGAF database are now included in the FIFRELIN cascades, in order to improve the description of the higher energy part of the spectrum. Furthermore, the angular correlations between $\mathrm{\gamma <!--\; ??\; -->}$ rays are now implemented in FIFRELIN, to account for the relative anisotropies between them. In addition, conversion electrons are now treated more precisely in the whole spectrum range, while the subsequent emission of X rays is also accounted for. The impact of the aforementioned improvements in FIFRELIN is tested by simulating neutron captures in various positions inside the STEREO detector. A repository of up-to-date FIFRELIN simulations of the Gd isotopes is made available for the community, with the possibility of expanding for other isotopes which can be suitable for different applications.