Space charge injection with electron beam irradiation for polyethylene and polypropylene films

The charging phenomenon in the dielectric materials often occurs in various radiation environments such as in the outer space and in the irradiation facilities. The irradiated charge accumulation in the dielectric materials can cause a permanent change on physical and chemical structure of the material which influences the electric properties of dielectric materials. In order to improve the reliability of dielectric materials, it is valuable to investigate the charging electrical properties of dielectric materials under radiation environment. In this work, penetration depths and distributions of irradiated charge in 250um thick polyethylene (PE) and polypropylene (PP) films after injection of 40 to 60keV electrons in vacuum environment were measured using a non-destructive and direct technique called Piezo-electric Induced Pressure Wave Propagation (PIPWP) method. This method enables us to observe the charge accumulating/dissipating process in real time. The comparison of experimental and analytical results reveals the difference between mean charge depth and migration process. The results also indicate that the various densities and depths of traps have significant effects on charge injection and migration process. The electrical properties of PE and PP were also studied after all original specimens were radiated by electron beam at last and some valuable results were obtained.