Comparison of neutron and gamma irradiation effects on KU1 fused silica monitored by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) studies have been carried out on KU1 fused silica irradiated with neutrons at fluences 1021 and 1022 n/m2, and gamma-ray doses up to 12 MGy. The effects of post-irradiation thermal annealing treatments, up to 850 deg. C, have also been investigated. Paramagnetic oxygen-related defects (POR and NBOHC) and E'-type defects have been identified and their concentration has been measured as a function of neutron fluence, gamma dose and post-irradiation annealing temperature. It is found that neutrons at the highest fluence generate a much higher concentration of defects (mainly E' and POR, both at concentrations about 5 x 1018 spins/cm3) than gamma irradiations at the highest dose (mainly E' at a concentration about 4 x 1017 spins/cm3). Moreover, for gamma-irradiated samples a lower treatment temperature (about 400 deg. C) is required to annihilate most of the observed defects than for neutron-irradiated ones (about 600 deg. C).