Induced conductivity of Mylar and Kapton irradiated by X-rays

The generalized use of polymeric materials in high radiation environments has increased the interest in processes of interaction between ionizing radiation and dielectrics, in particular in the radiation induced conductivity (RIC). Several papers have recently been published on the RIC of Mylar (Polyethylene-terephthalate-PET) [1–5]. In the present paper we show experimental results of an extensive investigation of RIC in Mylar and Kapton (Polyimide) irradiated by X-rays (tube voltage 55–95 (kV), at exposure rates X between 85 and 550R/sec, field strengths E between 1×10⁴–4.8×10⁵ V/cm, and sample thicknesses d between 6 and 75 μm. Measurements were carried out under a vacuum of 10⁻⁴ Torr at room temperature. Samples were circular foils of commercial materials. The surface of incidence carried an electrode of 4 cm diameter connected to the voltage source. The opposite surface carried a measuring electrode of k cm diameter and a guard ring of 6 cm internal diameter and 6.6 cm external diameter. Vacuum-deposited aluminium electrodes were used in all measurements reported here. Gold electrodes used in some cases were found to give higher current. Prior to irradiation, samples were poled for at least 10 min, to allow the absorption (dark) current to decay to a value small compared to the radiation-induced current.