临界堆中子增殖系数测量统计涨落数值模拟

Numerical simulation of statistical fluctuations in measurements of neutron multiplication coefficients on a critical power assembly

建立了临界堆中子增殖系数(α参数)计算模型,采用闪烁体加光电倍增管组成的电流型探测器对α参数进行测量。采用构造理想函数加统计涨落偏差的方式,利用数值模拟方法,研究了统计涨落对α参数测量结果的影响。结果表明:测量信号统计涨落会影响α参数测量精度;考虑统计涨落影响,为使α参数满足要求,需要使探测器入射粒子数达到一定数量;针对不同测量时间,入射粒子起始强度需要满足不同要求;当起始强度不能满足要求时,可以采用增加测量时间;指数信号带随机涨落时,较大的求值区间能有效减弱统计涨落的影响。

A computational model for the neutron multiplication coefficient （＂a value＂） of a critical power assembly is built, which is measured by current-mode detectors formed by scintillators and photomultiplier tubes （PMTs）. Through producing ideal functions and setting up various kinds o~ fluctuation errors, we numerally simulate the effects of statistical fluctuations in meas urements of the a values. The results indicate that precision of measuring the a values will be influenced by statistical fluctuations of the measured signals. Considering the influence of statistical fluctuations, the number of the incident particles to the detector~ s surface must reach a certain value in order to make the a value satisfy the measurement requirements. Thus the initial intensity of the incident particles must meet different requirements for different measuring time intervals, which can be increased while the initial intensity cannot meet the requirement. When the exponential signal carries random fluctuations with it, a larger time inter- val for maintaining the a values will effectively attenuate the influence of statistical fluctuations.