Charge buildup in polypropylene irradiated with monoenergetic electron beams

Charge buildup in 30-μm-thick films of polypropylene irradiated with monoenergetic electron beams of 10-45-keV energy is investigated. Using the split-Faraday cup, the mean charge depths at the beginning of electron injection, at the termination of injection, and 10 minutes after injection are measured. It is found that the depth increases with time during and after charging and depends on the 1.7th power of the electron energy. The depth increases also with the amount of injected charge. From the dynamics of charge motion during irradiation, the tradition-induced conductivity is determined a function of dose rate. It amounts to approximately 10^-14 (Ω·cm)^-1 at 10⁴ rad/s and is thus about an order of magnitude smaller than in Teflon