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Experiment Title: Study of Factors Determining the Radiation Sensitivity of Quartz Crystal Oscillators

Original Principal Investigator(s): Ahearn, Dr. John S. - Invest. Role: Original, Ahearn, Dr. John S. - Invest. Role: Present, Venables, Dr. John D. - Invest. Role: Original, Venables, Dr. John D. - Invest. Role: Present,

It has long been known that radiation increases the acoustic absorption of quartz crystal oscillators and produces shifts in their resonant frequency which may be as large as 400 parts per million. The need for high-precision quartz oscillator clocks (and filters) in communication satellites, missiles, and space probes makes it necessary to improve the radiation stability of materials used for these application.

Experiments performed at Martin Marietta Laboratories demonstrate that the technique of transmission electron microscopy (TEM) provides a powerful method for studying the effect of radiation on crystalline quartz. When suitably thin samples of alpha-quartz are examined by TEM, it is observed that defect clusters form at a rapid rate within the material even when the incident electron energy is as low as 20 keV. Recent evidence indicates that the clusters may actually be small amorphous regions in the crystalline material that grow larger with time under the electron beam created damage. Studies of this phenomenon indicate that the clusters are formed from atoms that have been displaced by electrons in the incident beam, that the clusters nucleate at impurities (because the cluster concentration appears to be impurity dependent), and that the clusters induce large strain fields in the lattice surrounding them, as evidenced by their paired black-dot images, which are characteristic of strain field contrast. The strain contrast that develops is caused by the strain associated with the misfit of the amorphous cluster and the crystalline matrix.

Two factors suggest that the observed clusters may be responsible for the radiation-induced frequency drift and acoustic-absorption effects associated with irradiated quartz resonators. First, the clusters are expected to be very effective in modifying the piezoelectric properties of quartz because the elastic properties of amorphous quartz are markedly different than that of crystalline quartz, and because of the large strain fields associated with the clusters. Second, both phenomena appear to be sensitive to the impurity concentration in the quartz material. If this conclusion is valid, it suggests that TEM can be used to classify grades of quartz according to their suitability for use in radiation-hard resonators. Moreover, using this technique it may be possible to identify the impurities that are responsible and thereby effect an improvement in the stability of quartz oscillators.

Photograph Classification: Flight

Associated Photograph(s):
LaRC - L90-10495
KSC - None
JSC - S32-89-013
LaRC - L84-07158
KSC - KSC-384C-317.01
JSC - None
LaRC - L92-17662
KSC - KSC-390C-731.11
JSC - None

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