中文摘要：

目的：模拟光子输运的过程，记录各相互作用和次级粒子对剂量计算的贡献，总结分析其对剂量贡献的大小。方法：PENELOPE程序包提供了模拟光子和电子输运的基本MC模块，基于所关心的物理问题本文对PENELOPE程序包进行二次编程，以在模拟过程中追踪光子输运详细过程，记录各相互作用及次级粒子对剂量的贡献。结果：首先研究在相同照射条件下，4种能量（10keV，100keV，1MeV，10MeV）的光子产生的中心轴剂量分布，次级粒子的软碰撞和硬碰撞产生的中心轴剂量分布，以及各级次级粒子的中心轴剂量分布；然后研究在相同照射条件下，4种能量（30keV，40keV，50keV，60keV）的光子产生的次级康普顿效应和次级光电效应对中心轴剂量分布。结论：不同能量下。次级电子软碰撞对于中心轴剂量的贡献起主要作用，次级光电效应对中心轴剂量的贡献随能量的增加而减小，而第一代次级粒子对于中心轴剂量的贡献大干其官代粒子的贡献．

英文摘要：

Objective： Simulating the photon transport process, recording the distribution of the dose which is caused by various of interactions and secondary particles, summarizing and analyzing the weightiness of each contribution. Methods： The PENELOPE package provides the basic Monte Carlo（MC） code which simulates the processes of photon and electron transport. Considering the concemed physical problems, the author modifies the PENELOPE program to simulate the track of photon transport process, meanwhile records the contribution of dose which is provided by various of interactions and secondary particles in this article. Results ： Firstly, in the same condition, recording the distribution from 4 source different energies （30 keV,40keV, 50 keV, 60 keV）, the distribution of the central axis total dose and the distributions which are caused by secondary Soft collision and secondary hard inelastic collision, and the distribution of the central axis dose provided by secondary particles. Secondly, in the same condition, recording the distribution of the central axis dose caused by secondary Compton scattering and secondary Photonelectric scattering. Conclusion： In different source of energy, the distribution of the central axis dose proffered by secondary soft collision play a major role; the contribution of secondary Photonelectric scattering decreased with the ascent of energy; the contribution from the first generation secondary particles is stronger than others.