Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Department of Engineering Physics

First Advisor

Briana J. Singleton, PhD.

Abstract

Multimode ytterbium-doped optical fibers (YDFs) are increasingly utilized in military applications involving fiber lasers and amplifiers. YDFs were irradiated with three different radiation sources (neutron, gamma, and mixed gamma/neutron) in order to determine the independent effects that gamma and neutron radiation have on the fibers. The transmission spectra of the fibers were measured during each irradiation and the spectral shapes and attenuation were compared at similar doses. Comparisons of the spectra showed that gamma radiation results in increased attenuation over the 550-975 nm wavelengths. Fast neutrons were found to contribute to increased attenuation near 500 nm. Neutron radiation also caused up to twice the amount of radiation induced absorption that gamma radiation did over all wavelengths in the spectrum measured from 500-1100 nm at the same dose. The spectrum from 980-1100 nm was the same shape between the fast neutron and gamma-only irradiations. This indicates that a 60Co source could potentially be used to approximate the effects on the operating range of YDFs resulting from fast neutrons. A recovery prediction model was also applied and evaluated against actual recovery data. It was found to be unreliable as an accurate predictor of the initial (∼ 15 minutes) recovery of YDFs exposed to a dose rate of 65 krad(Si)/hr neutron and 9 Mrad(Si)/hr gamma. By adjusting one parameter in the model to account for the initial faster rate of recovery, the model was able to closely approximate the recovery of the fibers after longer irradiations out to longer recovery periods.

AFIT Designator

AFIT-ENP-MS-16-M-057

DTIC Accession Number

Pending

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