Results 1 - 8 of 8
Results 1 - 8 of 8. Search took: 0.016 seconds
|Sort by: date | relevance|
[en] Optical properties of fluoride glasses make them attractive materials for optical transmission and low-loss optical fibers. In order to develop optical fiber systems in nuclear media, it is essential to observe the behavior of these fluoride glasses under irradiation. Only few data are available on this matter, and they are limited to bulk samples. This paper deals with the evolution of the optical transmission (from U.V. to mid I.R.) of ZBLA glass under radiation exposure
[en] The effect of γ radiations (cobalt 60) on the behavior of fluoride glass preforms and optical fibers was investigated in the range 0.2 to 3.0 microns. Optical losses decrease from the ultraviolet to infra-red region. Relaxation of irradiated fluoride glasses was observed, at room temperature, during heat treatment, and performed as function of time and temperature. An optical fiber made from an irradiated preform did not show any observable defects. The on-line irradiation of optical fibers allowed to measure the optical losses at 2.4 and 2.8 microns, likewise the influence of dose rate and relaxation. A characterization of defects induced by γ radiation on preforms had been realized by Electron Spin Resonance methods. A synthesis of results of different authors is presented. Possible mechanisms of degradation of fluoride glasses under γ exposure are discussed, and in particular the influence of oxygen impurities in the lattice
[fr]L'effet des rayonnements gamma sur des preformes et des fibres optiques a ete etudie avec un balayage spectral de 0.2 a 3.0 microns. Les pertes optiques decroissent de l'ultraviolet a l'infrarouge. Une relaxation des verres fluores irradies a ete observee; elle est fonction du temps et de la temperature. Les defauts induits par le rayonnement gamma ont ete caracterises par methode de resonance de spin electronique. Les mecanismes possibles de degradation sont discutes et en particulier l'influence des impuretes d'oxygene sur le reseau
[en] The effect of γ radiations (cobalt 60) on the behavior of fluoride glass preforms and optical fibers was investigated in the range 0.2 to 3.0 microns. Optical losses decrease from the ultraviolet to infra red region. Relaxation of irradiated glasses was observed, at room temperature, during heat treatment, and performed as function of time and temperature. An optical fiber made from an irradiated preform did not show any observable defects. The on-line irradiation of optical fibers allowed to measure the optical losses at 2.4 and 2.8 microns, likewise the influence of dose rate and relaxation. A characterization of defects induced by γ radiation on preforms had been realized by Electron Spin Resonance methods. A synthesis of results of different authors is presented. Possible mechanisms of degradation of fluoride glasses under γ exposure are discussed, and in particular the influence of oxygen impurities in the lattice
[fr]Le materiau etudie, du type ZBLA, est prepare par la Societe Le Verre Fluore sous forme de preformes et fibres optiques. Les irradiations sont effectuees a une temperature d'environ 400C, a l'aide d'irradiateurs au cobalt 60 dont les debits de dose sont de 4 000 gy.h-1 pour les preformes, et de 12 ou 120 gy.h-1 pour les fibres optiques. Les mesures d'absorption sur preformes sont effectuees sur un spectrophotometre de type Beckman 5740. Les mesures d'attenuations sur fibres sont realisees, pour un suivi en continu de la puissance optique transmise par la fibre. Ce dispositif de mesure permet un balayage spectral de 0,8 a 3 microns
[en] In order to develop infrared optical fiber systems in nuclear media, studies are made to know the behavior on line of fluoride glass optical fibers under irradiation. The increase of induced loss and the influence of the dose rate are given at 2.4 microns. Cycles of relaxation at room temperature and γ ray exposure allows an important bleaching and an unaffected kinetic of losses. Characterization of defects created by γ radiation on bulk of ZBLA glass is carried out by means of electron spin resonance (ESR). A linear kinetic of ESR signal with dose is observed and possible models for defects are discussed
[en] During the experiments carried out on the monitoring and the study of fish defrosting by an ultrasonic technique, we have difficulties in detecting the beginning of the thawing which is an important criterion of fish quality control. To address this problem, we use the Singular Value Decomposition method (SVD) which is a mathematical tool that permits to separate the high and low energies of an histogram. The image representing low energy signals indicates the start of the thawing by showing an echo that was hidden in the original image for cod fish. Using transducers for central frequencies above 500 kHz the observed results are not very good. Therefore, this method is suitable for fish which fat content is medium or low.
[en] ALGE3D is a three-dimensional hydrodynamic code which solves the momentum, mass and energy conservation equations. Its original purpose was to predict movement and dissipation of thermal plumes. To fill a gap in existing emergency response technology this code is being modified to predict the movement and dissipation of tracers as they interact with sediments and move between the dissolved and particulate phase. To increase the usability of the code a pre- and post- processing GUI have been developed to aid the user in developing the inputs for the code and processing the code output into understandable figures for decision makers.
[en] Ensemble modeling (EM), the creation of multiple atmospheric simulations for a given time period, has become an essential tool for characterizing uncertainties in model predictions. We explore two novel ensemble modeling techniques: (1) perturbation of model parameters (Adaptive Programming, AP), and (2) data assimilation (Ensemble Kalman Filter, EnKF). The current research is an extension to work from last year and examines transport on a small spatial scale (<100 km) in complex terrain, for more rigorous testing of the ensemble technique. Two different release cases were studied, a coastal release (SF6) and an inland release (Freon) which consisted of two release times. Observations of tracer concentration and meteorology are used to judge the ensemble results. In addition, adaptive grid techniques have been developed to reduce required computing resources for transport calculations. Using a 20- member ensemble, the standard approach generated downwind transport that was quantitatively good for both releases; however, the EnKF method produced additional improvement for the coastal release where the spatial and temporal differences due to interior valley heating lead to the inland movement of the plume. The AP technique showed improvements for both release cases, with more improvement shown in the inland release. This research demonstrated that transport accuracy can be improved when models are adapted to a particular location/time or when important local data is assimilated into the simulation and enhances SRNL's capability in atmospheric transport modeling in support of its current customer base and local site missions, as well as our ability to attract new customers within the intelligence community.
[en] The article is an overview of the research activity made in the framework of the Crystal Clear Collaboration aimed at obtaining scintillating glasses able to fit the constraints imposed for the active medium of the central Electromagnetic Calorimeter at CMS. The manufacturing of heavy metal fluoride glasses doped with Ce3+ is discussed. The luminescence and scintillation characteristics as well as the radiation hardness properties are extensively studied in the case of Ce doped fluorohafnate, found to be the most convenient glass scintillator for high energy physics applications. (orig.)