Evaluation of Mechanisms for Low-Dose Frequency Shifts in Crystal Oscillators

Two possible causes for the observed frequency shift of a crystal oscillator due to a small radiation dose to the crystal have been analyzed. Removal of mass from the surface of the crystal by the radiation does not appear to be a plausible cause for the frequency shift. However, the electric fields and voltages created in the crystal by charge that is photoemitted from the walls of the can around the crystal and is then trapped in the crystal are relatively large and could possibly produce the observed frequency shift. These trapped charges produce both normal and tangential electric fields inside the crystal. Consequently, the difference in this radiation-induced frequency shift for SC-cut resonators, which are primarily sensitive to normal stresses, and for AT-cut resonators, which are primarily sensitive to tangential stresses, is less than the difference in their normal voltage sensitivities.