伽马射线对低密度聚乙烯的空间电荷陷阱特征影响

为研究伽马射线辐照后的低密度聚乙烯材料在直流电场作用前后的空间电荷形成和衰减的陷阱特征,在60Co伽马射线的辐照源下得到最大辐照剂量为50 kGy的聚乙烯样品,利用电声脉冲法测量其空间电荷分布,进而提出了一种离散陷阱分布模型来解释射线辐照的空间电荷衰减特征。结果表明:在阴极附近出现异号的正电荷积累并随着辐照剂量增加而增加;分析认为射线辐照后样品出现的异号正电荷是由于材料发生了化学变化(氧化)而导致更深能级陷阱的产生;同时,利用所提出的模型计算了陷阱的能级深度和陷阱密度参数,并分析了它们与辐照氧化的微观机制。由陷阱能级和陷阱密度围成的曲线族变化可作为材料辐照老化的特征参量。

Influence of Gamma Irradiation on Space Charge Trapping Characteristics in Low Density Polyethylene

To investigate the role of oxidation in the formation and decay dynamics of space charge in gamma irradiated low-density polyethylene after being electrically stressed under dc voltage,polyethylene plaques were irradiated up to 50 kGy using a 60Co gamma source and space charge distributions were measured using the Pulsed electro-acoustic method.Furthermore,a model has been proposed to explain the decay dynamics of space charge.It has been found that a large amount of positive charge evolved adjacent to the cathode in the sample was clearly associated with oxidation of the surface.The amount of charge formed for a given applied stress increased with the dose absorbed by the material.It is believed that the slower decay rate of the positive charges is due to the oxidation by the irradiation in air which will produce more deep traps in the material.Furthermore,trap depths and their distributions are estimated by the simple trapping model to better understand the dynamics of space charge.It puts forward a characteristic representation method of material aging by gamma irradiation with changes of curve family that is constituted by curves of trap level and trap density.