Comparison Between Point Defect Generation by $\gamma$ -rays in Bulk and Fibre Samples of High Purity Amorphous

We compare the E ^´ , H(I) and Si-ODC(II) contents in a low-OH high-purity a-SiO₂ both in bulk and fibre forms. The investigation includes the effects of hydrogen loading of the fibre. We found that the H(I) centre appears during irradiation and that its concentration tends to increase with the dose in fibers impregnated with molecular hydrogen. For the hydrogen-treated fibers, no experimental repeatability could be found in the measurements of E ^´ and Si-ODC(II) although an acceptable agreement was still found in non-hydrogenated samples. This result suggests a possible complex reaction mechanisms under gamma radiation when the glass has a hydrogen excess.