Why do ordinary optical fibers quickly turn black and fail in nuclear power plants?
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In harsh environments with high ionizing radiation intensity, such as nuclear power plants, the phenomenon of ordinary optical fibers rapidly darkening and failing is primarily attributed to the Radiation-Induced Attenuation (RIA) effect in physical optics.
I. Physical Mechanism and Darkening Cause
Ordinary communication optical fibers (like the standard \text{G.652D} single-mode fiber) typically use silicon dioxide (\text{SiO}_2) as the core material, doped with germanium dioxide (\text{GeO}_2) to increase refractive index. When exposed to \gamma-ray, X-ray, or fast neutron radiation fields near nuclear reactors, the following microscopic processes occur:
- Chemical Bond Breakage and Defect Generation: High-energy radiation particles or photons penetrate the optical fiber, transferring ionization energy to the fiber lattice. This breaks the covalent bonds of \text{Si}-\text{O} and \text{Ge}-\text{O}, creating dangling bonds, free electrons, and holes.
- Formation of Color Centers: Free electrons or holes are trapped by lattice defects within the silica network and by dopants (such as germanium \text{Ge}, iron, OH groups, etc.), forming color centers with specific energy level structures.
- Light Absorption and Darkening: These color centers exhibit strong broadband absorption bands in the ultraviolet, visible, and near-infrared spectrum. Macro scopically, the fiber material’s absorption of visible light increases drastically, presenting a physical phenomenon of