Raman scattering and far infra-red absorption in neutron compacted silica

In vitreous silica, which has been compacted by irradiation with fast neutrons, the ultrasonic absorption, the excess heat capacity and the magnitude of the negative coefficient of thermal expansion decrease. In this work we report measurements of the far infra-red absorption and Raman scattering in such neutron compacted silica. These results are correlated with new measurements of ultrasonic absorption and thermal expansion in the same material. The results are consistent with an interpretation based on a decrease in the number of low-frequency modes.