Effect of gamma- irradiation on electrical breakdown stress of LDPE

摘要

Electrical breakdown stress of LDPE irradiated in a ~(60)Co γ-source at room temperature has been measured. It is believed that the changes in the electrical properties of the irradiated material derive from the changes in the physical and chemical state of the polymer compared to its pristine condition. It has been found that impulse breakdown stress is reduced perhaps due to those radiation-induced reactions resulting in more defects in the material. Irradiation in different environments has confirmed that oxidation can lead to further reduction in impulse breakdown stress. DC breakdown stress is closely associated with the space charge formation in the material. At low doses, the irradiation mainly causes the destruction of the crystalline spherulites, resulting in the formation of deep trapping centres in the material, leading to a lower carrier mobility and hence a higher breakdown stress. At high doses, oxidation increases and creates shallow trapping centres which increase the carrier mobility. The breakdown is affected by the trapped charge carriers which move quickly to the anode interface and build up a higher electric stress, resulting in the material failure at a low voltage. Changes in the β value after irradiation agree with the defect increase. Measurements of space charge distributions in both pristine and irradiated samples give direct evidence that space charge accumulated in the material strongly affects the electrical performance of the material. No space charge field is formed after irradiation.