Observation of a dose-rate dependence in the production of point defects in quartz

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Abstract
Electron-spin resonance (ESR) has been used to monitor the growth of aluminum-associated trapped-hole centers (i.e., [AlO4 ]0 centers) in high-purity cultured quartz during a sequence of irradiations with 1.7-MeV electrons. Production curves were obtained at three dose rates (3.6, 36, and 360 krad/min) for a series of crystals furnished by three commercial growers of quartz. The shape of each curve depended directly on the dose rate and the origin of the quartz; many of them had an initial rapid growth to a maximum concentration followed by a 5%–25% decrease as the number of defects approached an equilibrium value at a higher dose. We suggest that the complex shapes of these defect production curves, and also their variation between samples, is caused by a competition between the formation of [AlO4 ]0 centers and the formation of [AlO4 /H+ ]0 centers. At higher dose rates, in the 4–40 Mrad/min range, no dependence on dose rate was observed.