Irradiation of insulating polymer films with nonpenetrating electron beams results in lasting space charge. The charge-storage properties of polymer electrets are the most important for their application. The location of the charge and the radiation-induced conductivity are interesting both for production of foil electrets and for the investigation of charge phenomena in such materials. In this paper, charge buildup in 30 micrometers thick films of polypropylene irradiated with monoenergetic electron beams of 10 to 45 KeV energy is investigated. Using the split-Faraday cup, the mean charge depth at the beginning of electron injection, at the termination of injection, and 10 minutes after the injection are measured. It is found that the depth increase with time during charging, but decreases a little after the injection of electron beams. The charge depth also increases with the amount of injected charge. From the dynamics of charge motion during irradiation, the radiation-induced conductivity is determined as a function of dose rate.
"Charge buildup in polypropylene thin films", Proc. SPIE 1519, International Conference on Thin Film Physics and Applications, (1 November 1991); doi: 10.1117/12.47182; https://doi.org/10.1117/12.47182