Influence of radiation environments on space charge formation in γ-irradiated LDPE

Space charge profiles have been observed directly in irradiated LDPE using the PEA technique. There are marked differences between the charge characteristics of material irradiated in air and in vacuum and oxygen-free nitrogen gas. It is evident that the presence of oxygen during irradiation is essential for a significant amount of space charge to form in the irradiated LDPE. At low applied stress, a large amount of positive charges are present in the sample irradiated in air while only a small amount of charges exist in the samples irradiated in vacuum and oxygen-free nitrogen gas. At high applied stress charge injection takes place. In the case of samples irradiated in air, electrons injected neutralise with the positive ions, leading to significant reduction in space charge density. At low applied stress, space charge remaining in the sample can be used to assess the ageing taking place in the material