Physical property changes of crystalline and non-crystalline SiO2 due to neutron irradiation and recovery by subsequent annealing

Physical property changes of quartz and vitreous silica due to neutron irradiation and recovery by subsequent annealing were examined. Specimens were fast-neutron-irradiated up to a fluence of 3.0 × 1023 n/m2 at 140 °C, and 6.9 × 1023 n/m2 at 300 °C. Vitreous silica shrunk ∼0.8% in length after both irradiations. On annealing, the length started to increase above 200 and 500 °C for the lower and higher fluence specimens, respectively, and gradually increased with increasing annealing temperature. Quartz expanded in an anisotropic manner, with larger expansion along the a-axis as compared to the c-axis, due to the irradiation. Length and lattice parameter of quartz started to reduce for annealing over 300–500 °C, and were almost fully recovered at 800 °C in the lower fluence case, and 1000 °C in the higher fluence case. Thermal diffusivity reduced ∼10% in vitreous silica and 60–70% in quartz by the irradiation. Recovery of thermal diffusivity of vitreous silica and quartz by annealing resembled the corresponding length change.