Transient Change in Q and Frequency of At-Cut Quartz Resonators Following Exposure to Pulse X-Rays

Study of the transient behavior of AT-cut quartz resonators following pulse irradiation has been extended. In addition to 125 MHz 5th overtone crystal units previously reported, both 32 MHz and 5 MHz 5th overtone units have been studied using several different oscillator circuits, one of which is designed to give the transient resistance at series resonance, RS, as well as frequency as a function of time after pulse exposure. RS is proportional to the acoustic loss, i.e., Q-1, of the resonator. With but one notable exception, the annealing kinetics of the transient frequency offset following pulse irradiation obeys a t-½ relationship over three to four decades in time, indicative of a 1D diffusion limited trapping of uncorrelated mobile cation impurities in the crystal lattice. The most significant observations of the post-irradiation behavior of RS is the relatively large RS increase in natural quartz resonators. The transient increase anneals asymptotically to a relatively stable RS value which is somewhat higher than the pre-irradiation RS. The transient and steady-state post-irradiation change in RS is frequency dependent and, based upon the underlying model, should also be temperature dependent. The increase of RS in 5 MHz natural quartz resonators exposed to 104 Rad from the Sandia Laboratories' Hermes II facility is 30 times its pre-irradiation value at 0.2 sec after burst. However, RS for 32 MHz crystal units at .2 sec after exposure to 4 × 104 Rad typically increases only a factor of 2 times the pre-irradiation value.