Radiation effects on vibration spectra of silica

Full text: The radiation effects in spectroscopy of different modifications of silica are studied insufficiently and it is necessary to develop this investigations. In most cases authors examine the influence on luminescence and absorption of silica crystal or glass. They usually use small irradiation doses, different samples and different irradiation sources, mostly applying gamma-irradiation and ion implantation . In particular there is no exhaustive information about problem of neutron-activated phase transition in the crystalline silica by method of vibration spectroscopy, when the silica subjected to long time exposition in nuclear reactors channel. In this work nonlinear effects of light scattering in the crystalline modification silica (CS) at neutron-activated phase transition were studied. As a results of the high fluxes of fast neutrons bombardment the alpha-phase transformed into another crystalline phase. This process of radiation damage of crystalline structure has been studied by vibration spectroscopic methods. The vibration spectra were measured before and after irradiation with the fluxes (F) of samples. The influence of radiation on spectral characteristics of CS crystalline lattice of main vibrations: intensity R, frequency in region of low frequencies 100-400 cm-1 was studied. It is shown that neutron irradiation of crystals to the neutron fluxes from 1x1019 cm-2 to 1x1020 cm-2 strongly influences on their vibration spectra. Radiation effect on the parameters R, ν of lines in this region (at frequencies of 265(E), 357(A) cm-1) was determined. For example dose dependencies of spectral characteristics for the sort modes at 265(E) cm-1 are investigated. It can be seen from this curves that at the initial stage of irradiation these parameters change little. Noticeable changes of functions ν (F) and R(F) occur for F 1019 cm-2, when a rapid phase transition takes place. It is found that the both dose dependencies exhibit breaks and then at some critical point (Fc=7.1019 cm-2) these parameters are not registered, and one can see nonlinear changes of these curves. It was seen from the series of determined spectra that at this critical point spectroscopic parameters of lines are highly transformed and many bands disappear (for instance 265, 357 cm-1). It can be seen from curves Ri(F)-radiation changed for this modes to very non monotonously in the dose range, where according to XRD - X-ray diffraction methods of a data the phase of α-β transition occurs. The results on both lines (ν= 265(E), 357(A) cm-1) and for other lines are analyzed in comparison with the vibration spectra of the single crystal silica temperature dependence. It is supposed that in α -phase samples irradiated to fluxes near Fc the β-phase silica-like structure is formed, whereas at neutron-activated phase transition in the crystalline silica a high change of the inner vibration in SiO4 molecules is established. The work was done under the grant of Uzbekistan CST F-2.1.2 (author)