用蒙特卡罗方法和MATLAB计算冷屏内壁表面辐射光线落入探测器芯片的比例

介绍了用蒙特卡罗方法和MATLAB计算圆形冷屏内壁表面辐射落入探测器芯片比例的一种解决方案。该 方案基于三维空间中的方向数概念，首先利用MATLAB命令生成冷屏内壁表面上的随机点，再赋予该点一组随机方向数，获得 一条随机直线方程，以判断它是直接投向芯片平面还是经反射后投向芯片平面。对于反射的情况，根据镜面反射的性质及解析几 何公式，生成该直线在冷屏内壁上的反射光线，并判断它们是否落在探测器芯片区域。经统计后，可算出冷屏各部分落入芯片表面 的辐射光线在冷屏内壁表面发射出来的总光线数中所占的比例。该方法具有编程简单和方便实用等特点。

Calculating the Ratio of Radiation Rays Falling on Detector Chip from Inner Wall of Cold Shield with Monte Carlo Method and MATLAB

A method for calculating the ratio of the radiation rays falling on a detector chip from the inner wall of a circular cold shield by using the Monte Carlo method and MATLAB is presented. It is based on the directional number concept in three-dimensional space. First, a random point on the surface of the inner wall in the cold shield is generated with MATLAB. Then, a group of random directional numbers is associated to that point to form an equation for a random straight line and wether it is projected to the chip plane directly or to the chip plane after reflection is judged. In the case of reflection, the radiation rays reflected from the inner wall of the cold shield are generated according to the property of specular reflection and wether they fall on the chip region is judged. After statistical analysis, the ratio of the number of the radiation rays falling on the detector chip to the total number of the radiation rays emitted from the surface of the inner wall of the cold shield can be calculated. This method has the features of easy programming and simple operation.