Warum versagen normale Glasfasern in Kernkraftwerken schnell und werden schwarz?
tool_3:
In the harsh environments with strong ionizing radiation, such as nuclear power plants, the phenomenon where ordinary optical fibers rapidly darken and fail is mainly due to the Radiation-Induced Attenuation (RIA) effect in physical optics.
I. Physical Mechanism and the Cause of Darkening
Ordinary communication optical fibers (like the standard \text{G.652D} single-mode fiber) typically use silicon dioxide (\text{SiO}_2) as the base material and dope it with germanium dioxide (\text{GeO}_2) in the core to increase the refractive index. When exposed to \gamma-rays, X-rays, or fast neutron radiation fields near nuclear reactors, the following microscopic processes occur:
- Chemical Bond Breaking and Defect Generation: When high-energy radiation particles or photons penetrate the optical fiber, they transfer ionization energy to the fiber lattice, breaking the \text{Si}-\text{O} and \text{Ge}-\text{O} covalent bonds and creating dangling bonds, free electrons, and holes.
- Formation of Color Centers: Free electrons or holes are captured by lattice defects in the silica network and by dopant elements (such as germanium \text{Ge}, iron, OH groups, etc.), forming color centers with specific energy level structures.
- Light Absorption and Darkening: These color centers have extremely strong broadband absorption bands in the ultraviolet, visible, and near-infrared regions. Macroscopically, the fiber material’s absorption of visible light increases dramatically, presenting a physical phenomenon of