Charge dynamics for electron-irradiated polymer-foil electrets

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Abstract
Charge buildup, storage, and decay in 25‐μm polyfluoroethylenepropylene (Teflon type A) foils due to irradiation with partially penetrating monoenergetic electron beams in the 10–50‐keV range are investigated. Currents from the irradiated front surface and the nonirradiated rear surface are measured separately by means of 1000‐Å evaporated aluminum electrodes. Charge storage due to irradiation and a charge recall effect caused by irradiation of previously charged samples are observed. Discharge currents measured after termination of the irradiation indicate the importance of the delayed component of radiation‐induced conductivity. Measurements of the spatial depth of the charge are also reported. A mathematical model is developed which takes into account the radiation‐induced conductivity and the electrical and geometrical parameters of the sample. It allows for the calculation of current transients during and after irradiation.