Effects of Pulsed Ionizing Radiation on Some Selected Quartz Oscillator Crystals

The effects of high-energy ionizing radiation on the behavior and output frequency of electronic oscillators, whose frequency-determining elements were quartz crystals operating in the vicinity of 5 Mc, have been studied. Both fundamental- and fifth-overtone crystals were studied over a dose range from 3,000 rads (Si) to 2 Mrads (Si). The crystals studied were of two types: (1) standard commercial precision crystals fabricated from natural quartz with Q's of approximately 2.5 × 106 for the fifth overtone and 4 × 105 for the fundamental, and (2) special fifth-overtone crystals fabricated from swept pure Z-growth synthetic quartz. The natural quartz showed much larger changes in frequency and transient loss of Q than the swept synthetic crystals. The crystals were incorporated into commercial precision oscillator circuits and maintained in a temperature-controlled oven. The radiation doses (both 25-MeV electrons and 10-MeV peak bremsstrahlung gamma rays) were provided by the General Atomic electron linear accelerator. The radiation was collimated to irradiate only the crystal. The oscillator output signal was monitored with an oscilloscope during and after the radiation burst, and the frequency was measured by cycle counting for 10-or 100-sec time intervals. The precision of the frequency measurements was ±2 parts in 108 for the 10-sec intervals and ±2 parts in 109 for the 100-sec intervals. Electrons and gamma rays were shown to have the same effect on the crystals; therefore, most of the work was done with electrons because of the convenience of accumulating large doses in 4.5-psec pulses.