Measurement of dielectric properties in ceramics under ionizing and displacive irradiation conditions

Several experiments have been completed in which the dielectric properties of ceramic materials were measured during ionizing and displacive irradiation. The experimental matrix included single crystal sapphire, commercial-grade polycrystalline alumina, magnesium aluminate spinel, silicon nitride, and aluminum nitride. These materials are candidates for use in a number of fusion reactor components. The measurements were made at 100 MHz using a capacitively loaded resonant cavity. Essentially no affect: of ionizing radiation alone was observed for damage rates up to about 5×10⁵ Gy/h. However, pulsed fission reactor irradiation led to dramatic increases in the loss tangent. The fractional contributions of the ionizing and displacive fields to the total change observed during the neutron irradiations could not be unambiguously determined. The results of these experiments indicate that the use of postirradiation measurements leads to an underestimate of the radiation-induced dielectric degradation that occurs in the radiation field.