Rapid Annealing of Frequency Change in Crystal Resonators Following Pulsed X-Irradiation

Abstract

A transient negative frequency change in AT-cut 125 MHz 5th overtone quartz resonators has been observed following exposure to an intense burst of x-rays. All natural, Z-growth synthetic, and swept Z-growth synthetic resonators suffer a significant initial negative frequency offset. At room temperature, the transient frequency change in natural quartz anneals in approximately ten minutes to a relatively stable negative offset. For the synthetic quartz resonators, appreciable annealing of the initial negative offset continues for a longer period, finally arriving at an offset which may be positive in the case of the Z-growth synthetic but negligibly small for swept Z-growth synthetic. The transient frequency change is attributed to a relaxation process, which anneals above 165°K (Stage I). This annealable relaxation is superposed on a more stable part (Stage II) which is removed only by heating the crystal well above room temperature. The kinetics of Stage I annealing obeys a t-2 relationship and is interpreted in terms of a one-dimensional diffusion limited annealing of uncorrelated defects. In particular, it is proposed that the annealing involves the trapping of monovalent cations, most probably H+, at substitutional aluminum sites in the crystal lattice. The activation energy governing the diffusion of the defect to the trapping center is estimated to be 0.80 ± 0.05 eV.