Alpha-irradiation effects in SiO₂

Natural and synthetic crystalline α-quartz, as well as synthetic SiO₂ glass, were irradiated with different doses of 8.8 MeV He²⁺ ions. The irradiation-induced alteration was characterised using Raman and cathodoluminescence (CL) spectroscopy, optical microscopy, transmission electron microscopy (TEM) and CL and electron microscope imaging. The initially dull bluishviolet CL colour of the two α-quartz samples was found to be transformed to bright yellow in the irradiated areas. The emission maximum was observed 45 μm below the surface, which corresponds well with correlated helium trajectory lengths and defect density distribution. Both, total intensity and radial intensity distribution of the CL emission change with the irradiation dose. Observations suggest a nonlinear, approximately logarithmic increase of the CL intensity depending on the alpha dose. Significant broadening of Raman bands is only observed near the far end of helium trajectories. This broadening is not only caused by the structural radiation damage but also by strain between strongly and lowly damaged areas.