应用蒙特卡罗方法求解几何因子, 基于蒙特卡罗方法的几何因子计算程序使用C++语言编写, 可用于任意位姿的各种尺寸的圆面探测器对圆面源几何因子的计算。该程序使用了方差减小技巧。通过与国际通用蒙特卡罗计算程序(MCNP5)的计算结果对比, 该方法具有结果准确(误差较小)、计算速度快、使用方便等优点。最终使用该程序计算几何因子, 与实验数据进行对比, 成功验证了中子深度分布分析(NDP)能谱测量系统探测器位姿的准确性(误差5%以内), 并对其移动位置进行修正, 发现电机移动20 mm大约会产生1 mm的误差。

Geometric factor calculations play an important role in the absolute calibration of radioactivity measurement systems and in the determination of the activity of radioactive sources. The Monte Carlo method can always calculate the geometric factors when there is no analytical algorithm available for geometric factor calculations. Few papers have reported the calculations of geometric factors when source and detector are both disc, but are un-coaxial and un-parallel. The program in this study is based on the Monte Carlo method and is written in the C++ programming language, and it can be used to calculate the geometric factor of a disc detector for a disc source. The detector and the source can be any size at any cases. This program integrated a variance reduction method, by comparing. The results with that calculated using MCNP5. It can be concluded that the program calculates geometric factors accurately, fast and conveniently. The geometric factor calculation program verified the accuracy of the pose of the detector which was applied in the NDP energy spectrum measurement system; furthermore, it corrected the detector position roughly.