摘要
针对点堆动力学理论解释脉冲源法测试原理时存在的问题,基于无源中子输运方程分析次临界系统总中子数、泄漏γ射线计数率随时间的变化关系。理论分析表明:脉冲中子源作用结束后(无源条件下),在一定时间范围内,泄漏γ射线计数率和总中子数近似成正比,两者随时间变化服从近似指数衰减规律,反映系统本身的裂变衰减特性,可以由总中子数和γ射线计数率求解瞬发中子衰减时间常数。基于蒙特卡罗程序构造类Godiva裸铀球次临界系统,模拟脉冲中子源作用下中子和γ射线输运过程,计算总中子数、泄漏γ射线计数率及两者比值随时间的变化关系,结果与理论分析一致;利用脉冲源法由总中子数、泄漏γ射线计数率计算瞬发中子衰减时间常数α_(0),得到与α-k迭代一致的α_(0)。说明总中子数、泄漏γ射线计数率可以准确反映系统本身的裂变衰减特性。此外,根据理论分析和模拟计算给出脉冲源法可用数据的时间范围,分析泄漏γ射线计数率和总中子数比值的影响因素。
For problems of point-kinetic equation in explaining theory of the pulsed neutron source(PNS) method, evolution of neutron population and leakage γ-ray count rate of a subcritical system was analyzed with neutron transport theory. It is indicated that in a certain time range after the pulsed neutron source, the count rate of γ-rays leaked from the system is approximately proportional to the neutron population. And both of them change with time according to an exponential decay law, from which fission decay properties of the system can be deduced and the prompt neutron decay constant α_(0) can be calculated. To verify the theoretical analysis, a Godiva-like bare uranium-sphere subcritical facility with a pulsed neutron source at the center was modeled. Neutron and γ-ray transport process was simulated with a Monte Carlo code. Evolutions of neutron population, γ-ray count rate and ratio of them were obtained. They are consistent with theoretical analysis. With PNS method, prompt neutron decay constant α;is calculated. It is consistent with the α-k power iteration result, which indicates that the neutron population and leakage γ-ray count rate reflect intrinsic fission decay properties of the system accurately. In addition, a criteria of fitting time window for the PNS method is presented. Factors influencing the ratio of γ-ray count rate and neutron population are discussed.
作者
高屹
佘若谷
徐琪
GAO Yi;SHE Ruogu;XU Qi(Institute of Applied Physics and Computational Mathematics,Beijing 100094,China)
出处
《计算物理》
CSCD
北大核心
2022年第3期261-267,共7页
Chinese Journal of Computational Physics
基金
国家自然科学基金(11705012)资助项目。
关键词
脉冲源法
裂变衰减
瞬发中子衰减时间常数
次临界系统
中子诊断次临界实验
pulsed neutron source method
fission decay
prompt neutron decay constant
subcritical system
neutron diagnosed subcritical experiment
