Experimental evidence for two different precursors of E\u2019\u3b3 centers in silica

Electron paramagnetic resonance measurements of concentration and line shape of centers induced by \u3b3 ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two centers distinguishable by their line shape and having different precursors