An electric stress pulse technique for the measurement of charges in a plastic plate irradiated by an electron beam

The determination of the amount and distribution profile of charges in insulators has been studied by various methods, some of them utilizing thermal, mechanical and electrical stimulations. A new method incorporating pulse electrical stimulations and pulse acoustic detection is reported here, along with the preliminary results of the measurement of the amount and distribution profile of charges in electron-beam irradiated polymethyl methacrylate (PMMA) samples. The amount and the distribution of charges are obtained by the size and timing of acoustic signals produced in response to a high voltage impulse applied to the sample. Thus, determination of the profile of the spatial charge distribution in a sample became possible. A 5 mm thick PMMA plate irradiated with 1 MeV electrons at 0.5 −3.0 Mrads was found to trap charges of approximately −0.3 μC/cm2 at a mean depth of about 2 mm.