The present invention relates to an electron accelerator which is employed for sterilizing packaging material and which is included as part of an aseptic packaging machine which is intitially sterilized by means of an oxidizing chemical sterilizing agent such as H.sub.2 O.sub.2 and steam. A "window" of an electron accelerator, which is covered by metallic window foil, includes a thin coating of glass disposed on the window foil. The glass coating protects the window foil against chemical action such as oxidation resulting from the chemical sterilizing agent H.sub.2 O.sub.2.