Study on Radiation-induced Conductivity of Insulation Materials under High Electric Field

为了测试绝缘体的辐射感生电导率(RIG)，在室温下用DT中子和伽马射线对蓝宝石样品进行了辐照。在给定的偏置电压下，样品的辐射感应电流与辐射通量成正比。蓝宝石的Rig系数约为1×10~(-10)/Ω/m/Gy/S，并且在辐照开始时观察到很大的暂态电流。讨论了辐射感生电荷在绝缘子中的行为，并结合矿物绝缘(MI)电缆的脉冲X射线辐照实验结果进行了讨论。利用脉冲电荷测量系统很好地测量了电缆的电阻降低，电缆中心导线中感应的电荷与偏置电压和每脉冲X射线剂量近似成正比，这意味着电荷载流子(即电子)的漂移和产生率控制了电缆的退化。电缆绝缘体中电子的平均漂移长度估计约为15 nm(偏置电压100V，绝缘体厚度1.5 mm)。为了对绝缘体和MI电缆的退化进行详细的分析，我们需要基于泊松方程和精确的电子在绝缘体中的输运模型进行进一步的数值计算。

In order to examine the radiation-induced conductivity (RIG) of insulators, some sapphire samples were irradiated at room temperature with DT neutrons and gamma-rays. The radiation-induced current of the sample was proportional to the radiation flux under a given bias voltage. And the RIG coefficient of the sapphire was about 1 x 10^<-10>/Ω/m/Gy/s. Also, a large transient current was observed at the start of the irradiation. Behavior of radiation-induced charge in the insulator was discussed together with results of pulsed X-ray irradiation experiments on a mineral-insulated (MI) cable. The reduction of the electric resistance of the cable was well measured by use of the pulse-charge measuring system.The charge induced in the central wire of the cable was approximately proportional to the bias voltage and the X-ray dose per pulse, which means that the drift and production rate of charge carriers (i.e., electrons) dominates the degradation of the cable. The average drift length of electrons in the cable insulator (MgO) was estimated to be about 15 nm (bias voltage! 100V and insulator thickness! 1.5 mm). For the detailed analysis of the degradation of the insulator and the MI cable, we need further discussions with numerical calculations based on the Poisson's equation with a precise transport model of electrons in the insulator.