The widely held explanation for mechanical failure of silicate glasses rests upon the existence of Griffith-flaw and the associated free-ion diffusion concept used to model crack growth. However, this theory has consistently failed to provide complete agreement with the experimental results known to those "schooled" in the poignant literature. This dilemma coupled with the reports of single-valued strengths in fibers cannot be rationalized by the modification of the intrinsic Griffith-flaw distribution to essentially a delta function (this violates entropy). It is for these reasons that the field-enhanced ion diffusion model has been introduced. The inclusion of a term for electrostatic potential in the solution of Fick's second law is shown to be consistent with the experimental results in the existing literature. The results of the work presented herein provide further support of the proposed model, and the implied consequences of chemical corrosion in glass which results in its subsequent failure.

Measurements made on irradiated fibre optics at RMCS Shrivenham are reviewed and the less sensitive types of fibre are identified for various radiation conditions. Problems arising in relating these and other published results to specific applications are discussed.

The effect of y radiation (Co⁶⁰) on optical fibers is studied for investigations to remote measurement in irradiating environments. The spectral characteristics of PCS and AS silica fibers, PCS "wet" and AS "wet" and "superwet" are compared. An automatic computerized system for measurement "in situ" is used between 0.4 and 1,1 micron. Radiation-induced effects are examinated at 840 nm on PCS, AS with silicone, AS with epoxy (200 and 400/600m) up to 5.10⁸ rads. Samples of "dry", wet", "superwet" and "doped fluor" silica are studied up to 1,3.10⁹ rads between 0,3 and 2,5 μm. The photobleaching, the radiation hardening and the breakage of PCS and AS-silicone after 10⁷ rads are recognized. The spectral characte-ristics of a band at 610-630 nm, a spectral deformation at 945 nm for "wet" fibers and a peak of the radiation-induced attenuation are observed. The kinetic of the 630 nm defect in silica fibers and silica samples is also investigated.

The effect of y radiation (Co⁶⁰ ) on optical fibers is studied for investigations to remote measurement in irradiating environments. The spectral characteristics of PCS and AS silica fibers, PCS "Wet" and AS "wet" and "superwet" are compared. An automatic computerized system for measurement "in situ" is used between 0,4 and 1,1 micron. Radiation-induced effects are examinated at 840 nm on PCS, AS with silicone, AS with epoxy (200 and 400/6004m) up to 5.10⁸ rads.Samples of "dry", "wet", "superwet" and "doped fluor" silica are studied up to 1,3.10⁹ rads between 0,3 and 2,5μm. The photobleaching, the radiation hardening and the breakeage of PCS and AS-silicone after 10⁷ rads are recognized. The spectral characte-ristics of a band at 610-630 nm, a spectral deformation at 945 nm for "wet" fibers and a peak of the radiation-induced attenuation are observed. The kinetic of the 630 nm defect in silica fibers and silica samples is also investigated.

The radiation sensitivities of various fluoro-silica-clad step index fibers, and of germanium doped and of fluorine doped graded index fibers were measured in gamma and neutron fields. For the Fluosil types low sensitivities and a smooth dependence on the OH-content was found. Fluorine doping of the core seems not to degrade the radiation resistivity. During pulsed irradiation, a superposition of luminescense light and attenuation effects was observed. The luminescence light levels and the peak induced losses were measured as function of the gamma dose rate.

This study consists of measurements on effects of high energy electrons and X radiation in optical fibers. We compare the radiation damage behaviour of two pure silica core fibers with different claddings : a plastic clad silica fiber QSFA 100 μ (from F.O.I.) and a silica core F : doped silica clad fiber QSFAS 135 p(from The wavelength of interest is at 0,8 p. Two types of radiation source were used : pulsed, (linear accelerator and pulsed electron generator) and continuous (cobalt 60). With pulsed sources, data were acquired within 1 ps duration. From the experimental results that have been obtained, the PCS fiber appears to have a better radiation hardness than the all silica fiber. A "super wet" all silica fiber QSFAS 166 appears clearly to be less radiation sensitive than the "dry" all silica fiber QSFAS 135.

Attenuation spectra have been taken at 76 K and 195 K following a series of Co-60 irra-diation and photobleaching steps of all-silica fibers with both wet and dry pure silica cores. The photobleaching source, an AℓGaAs CW 820 nm emitting laser diode, caused significant attenuation recovery in all fibers at both temperatures over the entire measured wavelength range of 300 nm to 750 nm.

Experimental results are presented on the optical transmission properties of a pure fused silica core, polymer coated optical waveguide sheathed by three methodologies. The waveguides are examined during gamma ray (1.17, 1.33 MeV) exposure and at temperatures ranging from ambient to -60°C. Unsheathed optical waveguides, exposed previously, are reexamined and the effects of aging are compared to the sheathed examples.

The Idaho National Engineering Laboratory is actively involved in the development and application of fiberoptic-based sensor technology for use in nuclear reactor research. One such sensor is a minature fiberoptic probe which senses steam-to-water transitions in a high pressure, high temperature coolant circuit.' Hundreds of these probes have been utilized in non-nuclear reactor simulation facilities and efforts are underway to adapt these and other fiberoptic techniques to full-scale nuclear applications. This paper describes work recently completed to characterize fiberoptic attenuation induced by gamma and neutron radiation in a reactor. The specific goal was to make in-situ attenuation measurements of promising waveguide materials during radiation exposure at elevated temperatures characteristic of reactor environments. Testing was done in a swimming-pool-type reactor generating about one kilowatt thermal power and producing fluxes of about 10⁹n/cm²/sec fast neutrons (>1 MEV), 10¹⁰ on /cm2/sec thermal neutrons, and dose rates of 6 X 10⁶ rad/hr gamma radiation. Samples of state-of-the-art radiation-resistant waveguides, received from five manufacturers, were tested simultaneously. One set of waveguides was held at 180°C temperature and the other set remained at 20°C. Attenuation was monitored con-tinuously in several spectral bands in the 600-1050 nanometer region. Total reactor exposure time was about ten hours and the change in attenuation at this time for the heated samples was as low as 5 db/km at the longer wavelengths and as high as 3000 db/km at the shorter wavelengths. Attenuation in this range is acceptable for many instrumentation or sensor applications because transmission distances would be relatively short in the radiated region. The annealing effect at elevated temperature was found to be significant for all waveguide samples. A ten-fold decrease in attenuation was observed for one heated sample in comparison with its counterpart at ambient temperature (i.e., for 160oC temperature difference). Additional testing is underway in a 26-megawatt reactor facility. Higher dose rates, exposure times, and temperatures are planned.

Some applications of optical fibers require their exposure to intense radiation fields. This exposure can potentially degrade performance of a fiber data link. Research at Los Alamos National Laboratory has concentrated on development of an understanding of such radiation effects at short times, less than 100 ns.

The fluorescence and Raman emission spectra of optical fibers have been measured in samples that were either irradiated or presented a drawing-induced absorption. It is shown that the red band at 650 nm is centered at slightly different values and displays a different width in each case. Raman spectroscopy revealed the presence of molecular oxygen in fibers exhibiting the drawing-induced peak and a further emission at 695 nm was detected in one such fiber. These results emphasize the role of stoichimetry upon the characteristics of these fibers. It is suggested that excess 0₂ may form (0₂)₂ complexes that present emission bands in the same regions as the fibers.

Les spectres de fluorescence ainsi que les spectres Raman de fibres optiques ont ete en-registres a partir d'echantillons soit irradies, soit presentant une bande d'absorption apres etirage. Il a ete mis en evidence que le maximum de la bande de fluorescence dans le rouge se situe a des valeurs differentes. Dans chaque cas, une valeur differente de la largeur mi-hauteur de cette bande a ete observee. La presence d'oxygene moleculaire dans les fibres presentant un pic de fibrage a ete mise en evidence par spectroscopie Raman. Par ailleurs, une bande d'emission situee a 695 nm a ete detectee. Les resultats obtenus mettent en evidence le role joue par la stoechiometrie sur les caracteristiques optiques des fibres. La formation de complexes (0₂)₂ est suggere a partir d'un exces de molecules 0₂ dans les fibres. Ces complexes presentent des bandes d'emission dans les memes regions que celles observees dans les fibres.

In the United States, several public and private agencies have performed numerous radiation tests of fiber optic components and more specifically optical fibers. Even though the test procedures and test results have varied tremendously, several key parameters, such as radiation dose rate, temperature, and wavelength, have been identified. This paper compares some of the key parameters in the measurement of optical fiber radiation response and discusses standard radiation test practices. A generic radiation environment based on Glasstone's classic, The Effects of Nuclear Weapons, 1957, also is presented.

There were investigated the changes introduced by ionizing radiation in three different technological groups of optical fibres: i.MCVD low-loss and medium-loss optical fibres made from slightly doped high silica glasses for telecommunications purposes in UMCS Lublin, ii.PCS optical fibres designed for local area networks /LAN/ male by UMCS Lublin, iii.DC/TC optical fibres of high NA for instrumentation purposes, made from compound glasses by Glass Works Bialystok. Radiation investigations possessed completely different motivations for different groups of fibres. The basic aim of research referring to telecommunication fibres was: approximate determination of radiation sensitivity expressed in (d3/km.rad), looking for functional dependence between the quality of a fibre, its technological parameters and termical/radiation characteristics. Measurements of other fibres have been performed to gather directions concerning the problem how to increase this resistance against radiation environment. Following radiation characteristics have been presented and debated for three mentioned technological groups of optical fibres: spectral dependence of Losses for stated dose, attenuation dependence on dose and power of dose, relaxation processes, termically induced aniling processes, normalized radiation sensitivities.

Les avantages presentes par les liaisons a fibres optiques par rapport aux liaisons electriques classiques ont fait que leur utilisation, dans les environnements industriels et militaires fortement perturbes ou a haut risque de perturbation (champ electromagnetique, IEM, etc...), est de plus en plus frequente. Il semble donc naturel d'essayer d'etendre leur domaine d'utilisation a l'environnement nucleaire. L'expose qui va suivre traitera donc des resultats obtenus lors des essais d'irradiation gamma effectues d'une part sur des composants actifs (D.E.L, P.I.N) et d'autre part, sur des fibres optiques d'origines differentes et couramment utilisees.

Glass Optical Fibers are coated with organic coatings to provide physical protect and to preserve high strength. Specialized coatings are available for use as: 1. refractive index, plastic claddings; 2. soft (low modulus) buffers providing resista to microbending, and 3. tough, durable, secondary buffers for protection, long life easy cabling. New coatings are also available which provide a wide range of adhesion the glass allowing for a choice in removal techniques. This paper presents an overview of available organic coatings, their contributions the fiber producer and the end user and an indication of advances which can be expected the future. A comparison is made of relative cost factors and methods of cost reduction.

The generation of high-energy relativistic electron beam pulses in the range of 50 MeV, 10,000 A, and 10's of ns is accompanied by very large background radiation that makes diagnostic measurements difficult. Although conventional fast-response radiation detectors can be used, they are expensive, noise sensitive, and bulky. Diagnostic techniques using radiation-resistant optical fiber transmissions, however, provide great flexibility and immunity to electrical noise for carrying out electron beam monitor and control functions, characterization, and propagation studies. The use of optical fibers enables the sensitive recording apparatus such as microchannel plate detectors or imaging tubes or streak cameras to be located in a benign environment. A beam propagation optical diagnostic system has been developed which uses optical fiber links to observe luminescence produced by the electron beam interaction with air or with fast scintillators, and to transmit the beam signature to a remote location. Various fibers were evaluated for this application, and their selection criteria are discussed. The diag-nostic system employing the fibers and the experimental results obtained for various beam propagation conditions using a Febetron Flash X-Ray source are also presented.

The projected use of optical fibre is described to relay H_a light from the JET tokamak to a radiation-free environment. In the final two years of operation the device could produce through neutron emission an accumulated ionising dose of 1.5 x 10₈ rads(Si). The radiation-induced luminescence and optical absorption in the fibre are estimated. Whilst the former is negligible, the induced attenuation could reach 15 db. Photobleaching is an effective technique for reducing this loss. Continuous monitoring of the absorption, by transmitting a test signal through auxiliary fibres, would permit measurement of the absolute H_a intensity.

An optical measurement system will be presented which allows the continuous recording of radiation induced optical loss and thermoluminescence signals during and after irradiation. The complete optical system can operate in the spectral range from 0.6 to 1.7 μm. This allows the detection of the following absorption and scattering processes: elec-tronic transitions, Rayleigh-scattering and vibrational modes. Measurements on typical fibers will be shown. The measurements are performed in order to examine the influence of lowest exposure levels and to evaluate the application in dosimetry systems.