ABSTRACT For a subcritical reactor system driven by a periodically pulsed spallation neutron source in Kyoto University Critical Assembly (KUCA), the Feynman-α and the Rossi-α neutron correlation analyses were carried out to determine the prompt-neutron decay constant and quantitatively to confirm a non-Poisson characteristics of the neutron source. In these correlation analyses, a non-negligible contribution of delayed neutrons and a non-Poisson character of the source were considered, and each pulse was assumed to be a delta function. When a neutron counter was placed closely to the reactor core, the prompt-neutron decay constant determined from the present Feynman-α analysis well agreed with that done from a previous analysis for the same subcritical system driven by an inherent neutron source. However, the decay constant determined from the present Rossi-α analysis was in poor agreement with that done from the above previous analysis. This disagreement originated from an inevitable excitation of a higher mode. In the Rossi-α counting probability distribution, the excitation deformed a sharp cusp arising from the delta function to a smooth convex shape. When the data around the convex top were masked for least-squares fitting of the present Rossi-α formula, the disagreement could be successfully resolved. Compared with the previous Feynman-α and Rossi-α analyses under the Poisson inherent source, the non-Poisson spallation source definitely enhanced the respective prompt-neutron correlation amplitudes. The enhancement rate increased with an increase in subcriticality. Moreover, the Degweker’s factor (m 2-m 1 2)/m 1 2 of 0.067 ± 0.011, which indicated a non-Poisson character of the present spallation source, could be determined from the present correlation analysis and the non-zero value of the factor convinced us that the present source had a different statistical distribution from the Poisson.

中文翻译：

---

京都大学临界组件脉冲散裂中子源驱动的亚临界反应堆系统的 Feynman-α 和 Rossi-α 分析

摘要 对于京都大学临界装置（KUCA）中由周期性脉冲散裂中子源驱动的亚临界反应堆系统，进行了 Feynman-α 和 Rossi-α 中子相关分析以确定瞬发中子衰变常数并定量确认中子源的非泊松特性。在这些相关性分析中，考虑了延迟中子的不可忽略的贡献和源的非泊松特性，并且假设每个脉冲是一个 delta 函数。当中子计数器靠近反应堆堆芯放置时，根据目前的 Feynman-α 分析确定的瞬发中子衰变常数与先前对由固有中子源驱动的同一亚临界系统的分析得出的结果非常吻合。然而，根据目前的 Rossi-α 分析确定的衰减常数与上述先前分析确定的衰减常数不一致。这种分歧源于不可避免的更高模式的激发。在 Rossi-α 计数概率分布中，激发使由 delta 函数产生的尖峰变形为平滑的凸面形状。当凸顶周围的数据被当前 Rossi-α 公式的最小二乘拟合所掩盖时，分歧可以成功地解决。与之前在泊松固有源下的费曼-α和罗西-α分析相比，非泊松散裂源肯定增强了各自的瞬发-中子相关幅度。增强率随着亚临界度的增加而增加。此外，Degweker 因子 (m 2-m 1 2)/m 1 2 为 0.067 ± 0.011，