Radiation Induced Time Dependent Attenuation In A Fiber

Robert E. Kelly; Peter B. Lyons; Larry D. Looney

doi:10.1117/12.950962

15 April 1986 Radiation Induced Time Dependent Attenuation In A Fiber

Robert E. Kelly, Peter B. Lyons, Larry D. Looney

Proceedings Volume 0584, Optical Fiber Characteristics and Standards; (1986) https://doi.org/10.1117/12.950962
Event: 1985 International Technical Symposium/Europe, 1985, Cannes, France

Abstract

Characteristics describing the time dependent attenuation coefficient of an optical fiber during and following a very short and intense radiation pulse are analyzed. This problem is important for transmission applications when the fiber is subjected to gamma, electron, or neutron beams. Besides time, the attenuation coefficient is a function of temperature, dose rate, dose, nature of the radiation (n,e,y), fiber composition and purity, pre-existing solid state defects, and wavelength of the transmitted signal. The peak attenuation for a given fiber is mainly determined by the dose rate and pulse length, but temperature and strain (or athermal) annealing also contribute to a partial recovery during the pulse duration. The peak attenuation per unit dose appears to be smaller at high doses, perhaps caused by particle track overlap, which produces a saturation effect. After pulse termination, the attenuation coefficient tends to recover towards its pre-radiation value at different rates, depending upon the factors mentioned above. In particular, ionized electrons relax back to the positive lattice ions at a rate which depends upon initial separation distance and temperature. The initial separation distance is a function of beam energy. Some electrons will encounter a trap in the lattice and may recombine by quantum mechanical tunneling or be removed by photons (hence, absorption). Besides ionization, radiation may induce lattice displacements which in turn produce additional absorption centers. The displacement contribution has a different time constant than that associated with ionization. These topics, as they influence fiber characteristics, are discussed, along with supporting experimental data.

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Robert E. Kelly, Peter B. Lyons, and Larry D. Looney "Radiation Induced Time Dependent Attenuation In A Fiber", Proc. SPIE 0584, Optical Fiber Characteristics and Standards, (15 April 1986); https://doi.org/10.1117/12.950962

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