Low-Earth-orbit proton and gamma ionization effects in piezoelectric alpha quartz crystal resonators

Abstract

A bstructThe susceptibility of alpha quartz piezoelectric resonators to ionizing radiation manifests itself as frequency shifts. These frequency shifts degrade the performance of on-board satellite timing, navigation, and communication systems. Although , radiation shielding reduces this effect, high-energy protons (E > 65 MeV) can still interact with the piezoelectric quartz crystal lattice. The magnitude of the frequency shift in piezoelectric resonators is a function of dose and dose rate and also of the particle kinetic energy. Experiments showed that proton radiation represents the greatest hazard to piezoelectric quartz crystals. Electron radiation in low-earth orbits can be shielded by using approximately 3 gm/cm' of equivalent aluminum shielding. The radiation shields developed for these crystal resonators comprised low and high Z-shielding materials that reduce the amount of bremsstrahlung generated by the electrons. However, the magnitude of the proton radiation cannot always be reduced by shields because of weight considerations. Therefore, a study was initiated to investigate the interaction of proton radiation with the piezoelectric quartz crystals.These findings led to a study of the basic susceptibility mechanism in piezoelectric quartz crystal resonators and the development of low-earth-orbit radiation simulation tests using a proton cyclotron. The results of these studies are reported in this paper.To simulate the proton-radiation environment encountered by quartz crystals in space, one must model the energy spectrum of the proton radiation. A quantitative study of a lowearth orbit led to a proton-radiation model and the development of tests to simulate proton radiation using the Harvard University cyclotron [4]. A range modulator was designed for a specific curve of dose versus penetration depth in materials, so that protons could be deposited at specific depths in the piezoelectric resonator. Tests showed that the frequency shift per rad increased linearly as a function of proton kinetic energy over the 50-to 150-MeV range. Typically, the frequency shifts in the AT piezoelectric resonators were of the order of parts in IO " per rad for 100-MeV protons. I present below a modest explanation of this phenomenon in terms of the interaction of ionizing radiation with impurities in the crystal lattice and interface boundaries. I. INTRODUCTION 11. RESONATOR RADIATION STUDY The susceptibility of piezoelectric quartz crystal resonators to low-earth-orbit ionizing radiation degrades the performance of satellite communication systems. Previous studies have attempted to establish a relationship between the basic piezoelectric properties of quartz and its radiation response [l]. Some of these studies used the results of high dose (10 krad [Si]) tests to extrapolate the response of piezoelectric resonators to smaller doses (100 rad [Si]) encountered in low-earth orbits. Studies performed at The Johns Hopkins University Applied Physics Laboratory showed that the response of piezoelectric resonators to low do...