Radiation induced frequency offsets and acoustic loss in AT-cut quartz crystals

The acoustic loss and frequency versus temperature spectra are measured as a function of radiation dose for a number of matching Na-swept crystals and for H-swept AT-cut quartz crystals. As expected, large positive frequency offsets at both the upper and lower turnovers were observed for the Na-swept crystals. However, the magnitude of the offset was consistently much smaller than the change in height of the strong 53 K (5 MHz) Al-Na loss peak. This smaller offset was caused by a change in the `apparent´ angle of the crystal that comes about when the Al-Na center is replaced by the Al-OH or Al-hole center. The offsets of the swept crystals were usually smaller than those of the unswept samples. Only part of the observed fractional frequency offset at the turnovers could be explained by summing the heights of the loss peak changes. An additional radiation-induced offset was observed at temperatures below 15 K where the frequency versus temperature curves flatten out