低能中子在锆中产生的辐照损伤的计算机模拟研究

Computer simulation of radiation damage caused by low energy neutron in zirconium

以GEANT4为基础采用蒙特卡罗方法对能量为1MeV的中子在锆材料中的输运过程进行了模拟分析.首先计算得出:反冲核的能量主要分布在1keV和15keV之间,中子和靶核发生两次弹性碰撞的平均空间距离为29.47mm.由于中子和靶核在发生连续两次弹性碰撞过程中产生的两个反冲核能量较低,它们的空间距离又比较大,由此可以推测出:由初级离位原子产生的后续级联碰撞可以看做是一系列独立的子级联碰撞过程,同时也计算了中子在靶材的不同深度区域内产生的反冲核数目和平均能量.其次,利用蒙卡方法计算得到的结果,采用分子动力学方法,分别计算了五种不同能量下的初级离位原子产生的级联碰撞情况,给出了初级离位原子的能量与其产生的次级离位原子数目之间的关系以及不同能量下的初级离位原子产生的损伤区域范围等情况,通过蒙特卡罗方法和分子动力学方法的结合,给出了能量为1MeV的中子在锆材料中产生的初级辐照损伤分布图像.

Based on the Geant4 program-the package for simulating particle transportation in materials, simulations of the irradiation by neutrons with 1 MeV energy in zirconium were conducted The two adjacent elastic collisions between injected neutron and target atoms produce numerous primary knock-on atoms （PKA）. It is found that the average distance of adjacent collisions is 29.47 mm, and the kinetic energy of most PKAs ranges from 1 keV to 15 keV. The damaged area induced by the PKAs is in nanometer scale, which is far less than the distance between the two PKAs. According to the fact that, the subsequent cascade collisions caused by the two PKAs can be considered as a set of independent processes, it is reasonable to study the cascade collisions of the PKAs by means of molecular dynamics method. The cascade collision progress of PKAs with different energies was performed, and the number of interstitial atoms and the size of the damaged regions in the material were extracted. Through the combination of Monte Carlo method and molecular dynamics simulation, a complete physical picture of the primary damage caused by the 1 MeV neutrons in the zirconium was obtained.