The effects of neutron irradiation and temperature on optical fibers and materials

Anjali Singh, University of Rhode Island

Abstract

This thesis comprises of a study of the effects of neutron irradiation and temperature on optical fibers and materials. The first part of this thesis deals with the effects of neutron irradiation on optical fibers, detectors and potential fiber materials.^ The study of the effects of neutron irradiation on optical fibers revealed that loss of transmission occurs due to irradiation. This loss is dependent on the radiation dose and also depends on the composition of the fibers. Annealing of the irradiated fibers was used to determine the activation energy of the defects. The recovery at different temperatures could be explained by a thermal charge untrapping model, indicating that the damage caused is mainly due to ionization. The similarity of the mechanisms causing the damage due to neutron and gamma radiation are explained.^ The study of the effects of neutron irradiation on a silicon avalanche photodiode indicates that degradation occurs in the current gain of this device, at a number of different wavelengths. The degradation is found to increase with increasing dose. The multiplication noise, however, was found to decrease with increasing dose. The linearity of the device is maintained after irradiation. The signal to noise ratio was observed to be unaffected by the neutron irradiation.^ The second part of this thesis involves an investigation of the effects of temperature and neutron irradiation on the vibrational modes of alkaline-earth fluorides. The temperature dependence of the frequency and lifetime of the first order Raman active mode in the alkaline fluorides was measured in the range of $83\sp\circ K{-}500\sp\circ K.$ The phonon frequencies were found to decrease with temperature. The contribution to this shift due to anharmonicity was determined. The lifetimes of these modes were found to decrease with increasing temperature, indicating that mode coupling increases as the temperature increases.^ The effects of large fluences of neutron irradiation on the vibrational modes of CaF$\sb2$ were observed. It was found that even up to doses of 5 $\times$ 10$\sp{19}$ nvt, no additional vibrational modes are observed. The IR absorption edge, however, shifts to higher wave numbers (lower frequencies) with increasing dose. This is attributed to the presence of multiphonon absorption, occurring due to the lattice disorder caused by the irradiation. ^

Subject Area

Engineering, Electronics and Electrical|Engineering, Nuclear|Physics, Optics

Recommended Citation

Anjali Singh, "The effects of neutron irradiation and temperature on optical fibers and materials" (1992). Dissertations and Master's Theses (Campus Access). Paper AAI9239593.
http://digitalcommons.uri.edu/dissertations/AAI9239593

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