Effect of neutron irradiation on the optical properties and lattice dynamics of α-SiO2

The effect of reactor irradiation on the IR reflectivity spectrum of α-SiO2 single crystals is studied in a broad range of fast-neutron fluences. Data are presented on the irradiation-induced changes in the spectral characteristics of antisymmetric and degenerate vibrational modes of bridge bonds and in dynamic parameters. Critical lattice dynamics is revealed near the antisymmetric stretching and degenerate modes. The ionic polarizability and dynamic constants of the crystals are shown to be nonlinear functions of neutron fluence. The results are interpreted in terms of radiation damage, a radiation-induced phase transition, and breaking and stretching of some of the silicon-oxygen bonds. A mechanism of radiation-induced structural changes is discussed.

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