Rossi-α measurement is commonly used to determine the prompt neutron decay constant.The relation between prompt neutron decay constant and Rossi-α distribution are established on the condition of weak neutron source.When the source intensity is high, the measurment could not provide correct result, due to the overlap of neutrons emitted from different sources.In order to quantitatively analyze the influence of neutron source intensity on Rossi-α measurement, simulation tools to calculate the Rossi-α distribution are developed on the basis of MCNP code.In this paper, two sketch models of subcritical systems, a reactor model and an accelerator driven system model, are simulated to illustrate the relation between the estimated prompt neutron decay constant and the source intensity.Simulation results indicate that when the neutron source has high intensity, the calculated prompt neutron constant will deviate from the actual results.For both subcritical reactor and accelerator driven system models, when the intensity of the neutron source is low, the prompt neutron decay constant could be obtained by Rossi-α measurement, while, when the intensity is high, the measurement could not provide correct result of the constant.By studying the interrelationships of the source intensities and the measured results, the maximum usable intensity value which could provide correct measurement result could be obtained.It is possible to reduce the detection duration by choosing a relatively stronger usable neutron source within the range of the maximum usable intensity.%通过数值模拟手段研究了源强对Rossi-α测量的影响.为了定量研究中子源强对Rossi-α测量的影响,基于MCNP软件;开发了用于计算Rossi-α分布的数值模拟工具.反应堆模型和加速器驱动次临界系统的示意模型的数值模拟结果被用于展示瞬发中子衰减常数与源强之间的关联.数值模拟结果表明,入射源强源中子强度对Rossi-α测量结果有显著影响.对于处于次临界状态的反应堆和加速器驱动次临界系统模型,在入射源强较小时,Rossi-α方法可以正确给出反应堆中子衰减常数,但当入射源强较大时,测量不能给出正确的中子衰减常数.通过研究源强和测量结果的关系,可以找到能够给出正确测量结果的最大可用源强.通过选择一个可用源强范围内的较强中子源,可以减少测量所需时间.
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