Abstract The energy spectrum of the prompt-neutron flux at the Missouri University of Science and Technology Reactor (MSTR) was obtained using an activation method. Foils were irradiated at the bare rabbit tube (BRT) of the reactor core (which has a 120 W configuration). The neutron spectrum was determined using an unfolding method implemented in SAND-II code. The Monte Carlo N-particle (MCNP) model was used to calculate the spectrum at the bare rabbit tube, which was used as the initial guess for input into the SAND-II code. Various MCNP spectra with 620-, 143-, 89-, 50-, 22-, and 12-energy groups were used as the initial guess for input into SAND-II. Seventeen different foils were irradiated at 100 kW. The foil set covers energies from 0.025 eV to 13 MeV for a broad spectrum analysis. The photon counts for the activated foils were obtained using a high-purity germanium (HPGe) detector. The count results were input into the SAND-II code to predict the neutron flux spectrum for the MSTR. The spectra were collapsed into three groups: thermal, epithermal, and fast flux. With the 620-group initial guess, the thermal, epithermal, and fast neutron fluxes were 1.43 × 10 12 ± 2.82 × 10 11 n / c m 2 s , 4.51 × 10 11 ± 2.85 × 10 10 n / c m 2 s , and 5.38 × 10 11 ± 4.85 × 10 09 n / c m 2 s , respectively, giving a total flux 2.42 × 10 12 ± 3.02 × 10 11 n / c m 2 s . Disparities were noted in the distribution of the thermal and epithermal flux predictions, as the number of groups in the initial spectrum guess changed. The 59%/19% distribution of the thermal/epithermal flux, as predicted with the 620-group guess, is inconsistent with the 49%/26% distribution predicted with the 89- and 143-group guesses. The predictions based on the 89- and 143-group guesses are fairly consistent with the predictions obtained with the 22- and 50-group guesses. The 12-group initial guess resulted in the prediction of a fairly even distribution between the thermal (38%) and epithermal (36%) fluxes. Regardless of the number of groups in the initial guess, the SAND-II prediction is fairly consistent in the fast energy range. The fast neutron flux was found to range between 22% and 26%.

中文翻译：

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初始 MCNP 谱猜测对密苏里科技反应堆基于实验的中子谱确定的影响

摘要 利用活化方法获得了密苏里科技大学反应堆（MSTR）瞬发中子通量的能谱。箔在反应堆芯（具有 120 W 配置）的裸兔管 (BRT) 处进行辐照。中子谱是使用在 SAND-II 代码中实现的展开方法确定的。蒙特卡罗 N 粒子 (MCNP) 模型用于计算裸兔管处的光谱，用作输入到 SAND-II 代码的初始猜测。具有 620-、143-、89-、50-、22-和 12-能量组的各种 MCNP 谱被用作输入到 SAND-II 的初始猜测。以 100 kW 照射 17 个不同的箔片。箔组涵盖了 0.025 eV 到 13 MeV 的能量，用于广谱分析。使用高纯锗 (HPGe) 检测器获得活化箔的光子计数。计数结果被输入到 SAND-II 代码中以预测 MSTR 的中子通量谱。光谱被分为三组：热通量、超热通量和快通量。用 620 组初始猜测，热、超热和快中子通量分别为 1.43 × 10 12 ± 2.82 × 10 11 n / cm 2 s 、4.51 × 10 11 ± 2.85 × 10 10 n / cm 2 s 8 和 5。 × 10 11 ± 4.85 × 10 09 n / cm 2 s ，分别给出总通量2.42 × 10 12 ± 3.02 × 10 11 n / cm 2 s 。由于初始光谱猜测中的组数发生了变化，因此在热通量和超热通量预测的分布中注意到了差异。热/超热通量的 59%/19% 分布，如 620 组猜测所预测的，与使用 89 组和 143 组猜测预测的 49%/26% 分布不一致。基于 89 组和 143 组猜测的预测与使用 22 组和 50 组猜测获得的预测相当一致。12 组初始猜测导致对热流 (38%) 和超热流 (36%) 之间相当均匀的分布的预测。无论初始猜测中的组数如何，SAND-II 预测在快速能量范围内都相当一致。发现快中子通量在 22% 到 26% 之间。12 组初始猜测导致对热流 (38%) 和超热流 (36%) 之间相当均匀的分布的预测。无论初始猜测中的组数如何，SAND-II 预测在快速能量范围内都相当一致。发现快中子通量在 22% 到 26% 之间。12 组初始猜测导致对热流 (38%) 和超热流 (36%) 之间相当均匀的分布的预测。无论初始猜测中的组数如何，SAND-II 预测在快速能量范围内都相当一致。发现快中子通量在 22% 到 26% 之间。