EPR study of new defects in neutron irradiated KS-4V and KU1 fused silica

Electron paramagnetic resonance (EPR) studies have been carried out on high purity fused silica KS-4V (low OH content) and KU1 (high OH content), irradiated with fast neutrons (E > 0.1 MeV) at a high fluence of 1022 n/m2. The spectrum of irradiated samples shows various well-known types of paramagnetic defects, POR, NBOHC and E'. Their thermal stability has also been studied by heating the samples in air up to 775 deg. C. A detailed analysis of the spectra shows that the POR spectrum of neutron-irradiated KS-4V and KU1 has two contributions from centres POR(I) and POR(II), which show very different thermal annealing behaviour. POR(I) is identified with the POR centre previously reported, whereas POR(II) is associated to the effects of fast neutrons. Moreover, a new broad line centred at g = 2.02 is reported that we suggest could be associated to oxygen-hole centres in the neighbourhood of the high amount of tracks generated by ion displacement due to fast neutrons.