中子及次级γ在高空长距离蒙特卡罗输运模拟中的减方差方法  

A Varaince Reduction Method for Simulating the Long-Distance Transport of Neutrons and Secondaryγin High-Altitude Atmosphere by Monte Carlo Method

作　　者：刘利 左应红[1] 牛胜利[1] 朱金辉[1] 商鹏 李夏至 LIU Li;ZUO Yinghong;NIU Shengli;ZHU Jinhui;SHANG Peng;LI Xiazhi(Northwest Institute of Nuclear Technology,Xi’an 710024,China)

机构地区：[1]西北核技术研究所,西安710024

出　　处：《现代应用物理》2022年第1期26-33,55,共9页Modern Applied Physics

基　　金：国家重点研发计划资助项目(2020YF0709800)。

摘　　要：针对利用蒙特卡罗方法直接模拟计算中子及次级γ在高空大气中大空间长距离输运时遇到的有效粒子数太少、计算时间长及计算误差大等问题,建立了中子及次级γ在高空非均匀大气输运的几何模型,模拟了瞬发中子及次级γ在高空中长距离输运过程,并针对粒子输运特性开展了相应的减方差方法研究。通过对源偏倚、几何分裂、强迫碰撞、权窗、指数变换和DXTRAN球等减方差方法的比较研究发现,综合应用源偏倚、几何分裂和DXTRAN球的方法可有效降低中子及次级γ模拟结果的相对偏差,FOM因子分别提高了39倍和13倍。在此基础上,加入合理设置参数的时间分裂算法可进一步降低计算中子及次级γ时间谱的相对偏差。研究结果表明,综合应用源偏倚、几何分裂和DXTRAN球组合方法可得到20~40 km范围内的中子及次级γ射线注量,相对偏差小于1%,且FOM因子随粒子数的增加而趋于稳定。In Monte Carlo simulation of long-distance transport of neutrons and secondaryγin high-altitude atmosphere,the problems of small effective particle number,long calculation time,and large error will be encountered in direct calculation.In this paper,a geometric model of the transport of neutrons and secondaryγin the non-uniform high-altitude atmosphere is established,and the Monte Carlo simulation of long-distance transport of transient neutrons and secondaryγin high-altitude atmosphere is carried out.By comparing the different variance reduction methods of source bias,geometric splitting,forced collision,weight window,exponential transform,and DXTRAN,it is found that the methods of comprehensive application of source bias,geometric splitting,and DXTRAN can effectively reduce the relative deviations of the fluences of neutron and secondaryγ.The FOM factors of neutron and secondaryγare increased 39 times and 13 times,respectively.The time splitting algorithm with reasonable parameter setting can further reduce the relative deviation of time spectra of neutron and secondaryγ.The results show that the relative standard deviation of calculated neutron and secondaryγfluences in the range of 2040 km is less than 1%by using the methods of source bias,geometric splitting and DXTRAN,and the FOM factors tend to be stable with the increase of particle numbers.

关 键 词：减方差方法 中子及次级γ输运 高空大气 蒙特卡罗方法 

分 类 号：TL11[核科学技术—核能科学] O571[理学—粒子物理与原子核物理]