非均匀大气中γ射线输运的蒙特卡罗模拟方法

Monte Carlo Simulation of Gamma Ray Transport in Non-uniform Atmosphere

γ射线在高空大气中的输运问题常采用蒙特卡罗方法进行模拟,但由于大气是非均匀连续介质,通常需要根据高度上的密度变化将大气进行分层处理.高空大气密度变化非常剧烈,精细的分层会带来很大的计算量.针对非均匀连续介质中的粒子输运问题,利用质量距离抽样方法代替传统的步长抽样方法,提出一种可直接模拟粒子在非均匀连续介质中输运的蒙特卡罗方法,实现γ射线在非均匀大气中输运的蒙特卡罗模拟,并与MCNP程序的计算结果进行比较,结果符合较好.

The atmosphere is a kind of non-uniform media, whose density drops rapidly with the increase of height. In order to simulate transport of gamma ray in high-altitude atmosphere, the media is divided into many uniform layers with different densities. To eliminate error, the number of layers should be as many as possible,which results in a large amount of computation. We propose a method without layering. It samples mass distance to replace step length of particles. The results agree well with those calculated directly by MCNP code. The method increases speed of computation considerably.