Steady-State and Transient Radiation Effects in Precision Quartz Oscillators
Radiation effects on 5 MHz 5th overtone AT cut Premium-Q quartz resonators are evaluated, comparing sweeping processes and resonator fabrication procedures. The resonators were irradiated at operating temperatures in oven controlled oscillator test beds with pulsed 10 MeV electrons from 200 rads up to 1 Mrad as well as with continuous 60Co gamma rays. Steady-state (permanent) and transient radiation-induced frequency changes were measured, the persistence of radiative preconditioning was investigated and the effect on drift rate was evaluated. From saturation characteristics of the steady-state frequency offset as function of total electron dose, the formation rate cross sections of several radiation-induced crystal defects have been evaluated. Formation of at least one defect is sensitive to differences in the sweeping process. In some resonators, frequency recovery after irradiation is dominated by an exponential decay mechanism with a time constant of 3.7 days. Under continuous gamma ray exposure with dose rates between 10 and 90 rad/hour, the frequency response is characterized by a steep initial rise followed by different patterns of saturation and recovery.