A Light Bulb Moment for Radiation Induced Conductivity of Polyether-etherketone

Dielectric materials are important in myriad applications from high voltage DC power transmission to spacecraft charging. The conductivity of these dielectric materials can be the difference between a successful space mission and catastrophic failure of a satellite. It is important to know both a material's electrical conductivity at equilibrium as well as the effects of radiation, as radiation can change conductivity by orders of magnitude and space is a harsh environment. The electrical conductivity at equilibrium can be measured via constant voltage conductivity (CVC) measurements, where a sample is placed in a parallel plate capacitor configuration, a voltage is applied, and a current is measured. Similarly, the effects of radiation on conductivity, or radiation induced conductivity (RIC), can be measured in the same manner while simultaneously irradiating a sample, e.g. with high energy electrons. A RIC system was built in the Materials Physics Group at Utah State University. The system was tested for its capabilities for performing CVC measurements in addition to RIC measurements. During testing on an 18 µm thick polyether-etherketone (PEEK) sample, some seemingly spurious data was obtained. There were, what appeared to be, arbitrary peaks of increased current throughout the data. Through careful cross-referencing of measured environmental data in the laboratory during the measurements, it was discovered to be photo-induced conductivity due to ambient light. The ambient light caused an increase in the current of just a few fA's. This effectively resulted in a measurement of the radiation induced, or photo-induced, conductivity due to ambient light shining on PEEK.