An electron spin resonance study was made of the defects which were introduced by the γ-irradiation of various types of natural and synthetic silica. Three main structures were identified. These were the E’ center and 2 doublets with field splittings of 7.4 and 11.8mT; both centered around the E’-center signal. Another structure which partially overlapped the E’ center line was also detected. This consisted of 3 peaks with a maximum field splitting of 1.36mT. An investigation was made of the growth kinetics of these centers with increasing accumulated γ-ray dose. In all of the materials investigated, the growth of E’ centers could be interpreted as being caused by the activated conversion of one or more precursors. The 1.36mT structure could be considered to be a hyperfine structure of the E’ centers which were generated by the same precursors but interacted with a nuclear spin. The 7.4mT doublet exhibited sub-linear growth, as a function of γ-ray doses ranging from 0.01 to 1000Mrad, and a direct correlation with the γ-ray induced photoluminescence band at 4.4eV. The 11.8mT doublet was generated only in natural silica samples, and could be related to γ-ray induced bleaching of emission bands at 3.1 and 4.2eV.

Creation of Paramagnetic Defects by Gamma Irradiation in Amorphous Silica. S.Agnello, R.Boscaino, M.Cannas, F.M.Gelardi: Applied Magnetic Resonance, 2000, 19[3-4], 579-85