The influence of gamma radiation on space charge formation in low-density polyethylene

Energetic ionising radiation can alter the chemical structure of polymeric materials by various mechanisms and may also give rise to the presence of trapped charge within the material, the trapping characteristics of which can be influenced by these radiation-induced structural alterations. In the present work, the formation of space charge in irradiated low-density polyethylene (LDPE) was investigated using a laser-induced pressure pulse (LIPP). Specimens of LDPE, 350 μm thick, were irradiated in a ⁶⁰Co γ-source in room air to various doses and the results indicate that space-charge distributions are dependent on both dose and applied electric stress, including the length of time for which the stress is applied. For example, at a dose of 10 kGy or less a stress of 25 kV/mm results in an abundance of positive charge adjacent to the cathode. As the stress is increased to 60 kV/mm the positive charge extends to the anode. At doses above 50 kGy, however, charge formation within the dielectric becomes more complicated in that as well as having positive charge adjacent to both electrodes there can be a substantial negative charge in the middle of the test specimen