HPGe探测器死层厚度及点源效率函数研究

Dead layer thickness and efficiency function of point source for HPGe detector

在层析γ扫描分析方法的效率矩阵求解过程中,建立准确尺寸的HPGe晶体计算模型对所求的探测器效率矩阵准确性有很大影响。在使用原始的实验探测器晶体尺寸建立的模型进行探测效率计算时,发现计算与实验所得的探测效率最大误差达19%。调整探测器计算模型的死层厚度可使计算结果准确度得到很大改善。研究发现,死层厚度与各测量点相对误差平均值存在线性关系,在此基础上提出一种可快速确定最优死层厚度的修正方法。使用调整后探测器晶体尺寸,计算出不同位点源位置不同射线能量下的探测效率,拟合出探测效率与点源位置及射线能量的函数关系,用于快速求得探测效率矩阵。

The efficiency matrix calculation of tomographic gamma scanning technique can be affected severely by HPGe crystal model used in the Monte Carlo simulation. With the producer-provided dead layer thickness, the calculated detector efficiency is up to 119% larger than the measured efficiency. By adjusting the dead layer thickness, the relative error could be minimized. A linear correlation between the dead layer thickness and the average relative error was established. With the corrected geometry of HPGe detector, the spatial efficiency of the detector under the radioactive point source is studied and the function, which could be used to calculate the efficiency matrix quickly between the detection efficiency, radiation energy and the position of the point source.