Search results for "silica"
showing 10 items of 1092 documents
Optical frequency domain reflectometer distributed sensing using microstructured pure silica optical fibers under radiations
2016
International audience; We investigated the capability of micro-structured optical fibers to develop multi-functional, remotely-controlled, Optical Frequency Domain Reflectometry (OFDR) distributed fiber based sensors to monitor temperature in nuclear power plants or high energy physics facilities. As pure-silica-core fibers are amongst the most radiation resistant waveguides, we characterized the response of two fibers with the same microstructure, one possessing a core elaborated with F300 Heraeus rod representing the state-of-the art for such fiber technology and one innovative sample based on pure sol-gel silica. Our measurements reveal that the Xray radiations do not affect the capaci…
Formation and accumulation of radiation-induced defects and radiolysis products in modified lithium orthosilicate pebbles with additions of titanium …
2016
Abstract Lithium orthosilicate (Li4SiO4) pebbles with 2.5 wt.% excess of silicon dioxide (SiO2) are the European Union's designated reference tritium breeding ceramics for the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM). However, the latest irradiation experiments showed that the reference Li4SiO4 pebbles may crack and form fragments under operation conditions as expected in the HCPB TBM. Therefore, it has been suggested to change the chemical composition of the reference Li4SiO4 pebbles and to add titanium dioxide (TiO2), to obtain lithium metatitanate (Li2TiO3) as a second phase. The aim of this research was to investigate the formation and accumulation of radiation-induced …
Comparison Between Point Defect Generation by $\gamma$-rays in Bulk and Fibre Samples of High Purity Amorphous ${\hbox {SiO}}_{2}$
2008
We compare the E', H(I) and Si-ODC(II) contents in a low-OH high-purity a-SiO2 either in bulk or fibre forms. We found that the H(I) centre appears during irradiation and tend to increase with the dose if the fibre contains hydrogen excess. This behaviour is believed to be one the possible reason to explain the apparent radiation-sensitivity enhancement in the blue-UV spectrum when the fibre is hydrogenated and irradiated at high dose. However for the hydrogen-treated fibres, no experimental repeatability could be evidenced in the measurements of E' and Si-ODC(II) although an acceptable agreement was still found in normal samples. This suggests a possible complex reactional mechanisms in pr…
Radiation effects on silica-based preforms and optical fibers-II: Coupling ab initio simulations and experiments
2008
International audience; Abstract—Experimental characterization through electron paramagnetic resonance (EPR) and confocal luminescence microscopy (CML) of a Ge-doped glass (preform and fiber) reveals the generation of several point defects by 10 keV X-ray radiation-induced attenuation: GeE', Ge(1), Ge(2), and Ge-ODC. The generation mechanisms of Ge-ODC and charged defects like GeE' centers are studied through ab initio simulation. Our calculations used a 108 atom supercell with a glass composition comparable to the Ge-doped core or to the pure-silica cladding of the canonical sample. The large size of our cell allows us to study the influence of the local environment surrounding the X-ODC d…
Steady-State X-Ray Radiation-Induced Attenuation in Canonical Optical Fibers
2020
The so-called canonical optical fibers (OFs) are samples especially designed to highlight the impact of some manufacturing process parameters on the radiation responses. Thanks to the results obtained on these samples, it is thus possible to define new procedures to better control the behaviors of OFs in radiation environments. In this article, we characterized the responses, under steady-state X-rays, of canonical samples representative of the most common fiber types differing by their core-dopants: pure silica, Ge, Al, and P. Their radiation-induced attenuation (RIA) spectra were measured online at both room temperature (RT) and liquid nitrogen temperature (LNT), in the energy range [~0.6…
Solidification of ion exchange resins saturated with Na+ ions: Comparison of matrices based on Portland and blast furnace slag cement
2017
International audience; Ion exchange resins (IERs) are widely used by the nuclear industry to decontaminate radioactive effluents. After use, they are usually stabilized and solidified by encapsulation in cementitious materials. However, for certain combinations of cement and resins, the solidified waste forms can exhibit strong expansion, possibly leading to cracking of the matrix. In this work, the behaviour of cationic resins in the Na$^+$ form is investigated in Portland cement (CEM I) or blast furnace slag cement (CEM III/C) pastes at early age in order to have a better understanding of the swelling process. The results show that during the hydration of the CEM I paste, the resins exhi…
Time resolved photoluminescence associated with non-bridging oxygen hole centers in irradiated silica
2008
Abstract We report time resolved photoluminescence spectra of irradiated silica under excitation with a laser tunable in the visible and UV range. The investigated samples exhibit the emission band at 1.9 eV associated with non-bridging oxygen hole centers, whose spectral and kinetics properties do not depend on the kind of irradiation (γ, β and neutrons). The 1.9 eV luminescence decay follows a multi-exponential curve with a characteristic lifetime that increases from 8.9 μs to 10.4 μs on increasing the emission energy. This dependence accounts for the blue-shift of the emission band during its decay and is interpreted as due to the inhomogeneous properties of silica leading to a distribut…
Influence of the manufacturing process on the radiation sensitivity of fluorine-doped silica-based optical fibers
2011
International audience; In this work, we analyze the origins of the observed differences between the radiation sensitivities of fluorine-doped optical fibers made with different fabrication processes. We used several experimental techniques, coupling in situ radiation-induced absorption measurements with post mortem confocal microscopy luminescence measurements. Our data showed that the silica intrinsic defects are generated both from precursor sites and from strained regular Si-O-Si linkages. Our work also provides evidence for the preponderant role of the chlorine in determining the optical losses at about 3.5 eV. The results show that the manufacturing process of these fibers strongly af…
Irradiation induced defects in fluorine doped silica
2008
International audience; The role of fluorine doping in the response to UV pulsed laser and c radiation of silica preforms and fibers was studied using electron spin resonance (ESR) spectroscopy. Exposure to radiation mainly generates E0 centers, with the same effectiveness in fibers and in preforms. The E'concentration in F-doped silica fibers is found to increase with UV energy fluence till a saturation value, consistently with a precursor conversion process. These results show the fluorine role in reducing the strained Si–O bonds thus improving the radiation hardness of silica, also after drawing process.
Nucleation and crystal growth in a suspension of charged colloidal silica spheres with bi-modal size distribution studied by time-resolved ultra-smal…
2014
A suspension of charged colloidal silica spheres exhibiting a bi-modal size distribution of particles, thereby mimicking a binary mixture, was studied using time-resolved ultra-small-angle synchrotron X-ray scattering (USAXS). The sample, consisting of particles of diameters d(A) = (104.7 ± 9.0) nm and d(B) = (88.1 ± 7.8) nm (d(A)/d(B) ≈ 1.2), and with an estimated composition A(0.6(1))B(0.4(1)), was studied with respect to its phase behaviour in dependance of particle number density and interaction, of which the latter was modulated by varying amounts of added base (NaOH). Moreover, its short-range order in the fluid state and its eventual solidification into a long-range ordered colloidal…