Normalization of ToF (n,f) Measurements in Fissile Targets: Microscopic cross-section integrals

IF 2.8 1区 物理与天体物理 Q2 PHYSICS, NUCLEAR
I. Durán , R. Capote , P. Cabanelas
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However, many ToF experiments do not collect data down to the thermal energy and use normalization cross-section integrals defined at different arbitrary energy intervals. Normalization fission cross-section integrals <span><math><msub><mrow><mi>I</mi></mrow><mrow><mn>3</mn></mrow></msub></math></span> are recommended in between-valleys energy regions 8.1–14.7 eV, 7.8–11 eV, 9–20 eV, and 11.7–19.5 eV for fissile targets <sup>233</sup>U, <sup>235</sup>U, <sup>239</sup>Pu, and <sup>241</sup>Pu with values equal to 689.0(10.8), 245.7(4.1), 1059(6), and 1378(33) <span><math><mi>b</mi><mo>⋅</mo><mi>e</mi><mi>V</mi></math></span>, respectively. 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引用次数: 0

Abstract

Precise normalization of ToF yield measurements of neutron induced fission in fissile targets is challenging, but the appropriate normalization is also of critical importance for nuclear energy and criticality safety, among other applications. A typical normalization relies on the Thermal Neutron Constants (TNC) recommended at the thermal point (fission σf0 and capture σγ0 thermal cross sections) by the Neutron Standards. However, many ToF experiments do not collect data down to the thermal energy and use normalization cross-section integrals defined at different arbitrary energy intervals. Normalization fission cross-section integrals I3 are recommended in between-valleys energy regions 8.1–14.7 eV, 7.8–11 eV, 9–20 eV, and 11.7–19.5 eV for fissile targets 233U, 235U, 239Pu, and 241Pu with values equal to 689.0(10.8), 245.7(4.1), 1059(6), and 1378(33) beV, respectively. The 235U normalization integral I3 derived in this work of 245.7(4.1) beV is in good agreement within quoted uncertainties with the Neutron Standards value of 247.5(3.0) beV.

Additional cross-section integrals I1 in the thermal region from 20–60 meV are derived to fix both the normalization and the slope of the fission cross section at the thermal point providing additional constraints for R-matrix evaluations of experimental fission yields. Ratios σf0/I1 and I3/I1 feature very low uncertainty due to the strong positive correlations between the numerator and the denominator and are comprehensively derived for the first time. Integral ratios I3/I1 of 39.31(54), 13.08(20), 41.65(22), and 40.46(85) are recommended as reference for fissile targets 233U, 235U, 239Pu, and 241Pu, respectively. Similarly, ratios σf0/I1 of 30.40(18), 31.22(12), 29.58(7), and 29.95(35) are also recommended as reference for corresponding fissile targets. These recommended ratios can be used by experimentalists to normalize their measured thin-target fission yield data, but also by evaluators to constrain their R-matrix analysis that use multiple sets of measured data renormalized as recommended in this work.

An evaluation of thermal (n,f) cross sections σf0 presented in this work for all fissile targets is in excellent agreement with the Thermal Neutron Constants defined in the Neutron Standards within one-sigma uncertainty. Such agreement guarantees the reliability of our new evaluation of reference integrals based on the whole database of consistent experimental TOF data.

裂变目标中 ToF (n,f) 测量的归一化:微观截面积分
对裂变目标中子诱导裂变的 ToF 收率测量进行精确归一化具有挑战性,但适当的归一化对于核能和临界安全等应用也至关重要。典型的归一化依赖于中子标准在热点(裂变 σf0 和俘获 σγ0 热截面)推荐的热中子常数 (TNC)。然而,许多 ToF 实验并不收集低至热能的数据,而是使用在不同任意能量区间定义的归一化截面积分。对于易裂变目标 233U、235U、239Pu 和 241Pu,建议在 8.1-14.7 eV、7.8-11 eV、9-20 eV 和 11.7-19.5 eV 间隔能量区使用归一化裂变截面积分 I3,其值分别等于 689.0(10.8)、245.7(4.1)、1059(6) 和 1378(33) b-eV。本研究得出的 235U 归一化积分 I3 为 245.7(4.1) b-eV,在引用的不确定度范围内与中子标准值 247.5(3.0) b-eV十分吻合。在 20-60 meV 的热区还得出了额外的截面积分 I1,以固定热点处裂变截面的归一化和斜率,为实验裂变产率的 R 矩阵评估提供额外的约束条件。由于分子和分母之间的强正相关性,σf0/I1 和 I3/I1 的比率具有极低的不确定性,并且首次得到了全面的推导。建议将积分比 I3/I1 分别为 39.31(54)、13.08(20)、41.65(22) 和 40.46(85),作为裂变目标 233U、235U、239Pu 和 241Pu 的参考。同样,σf0/I1 的比率为 30.40(18)、31.22(12)、29.58(7) 和 29.95(35),也被推荐作为相应裂变目标的参考。实验人员可以使用这些推荐比率对他们测量的薄靶裂变产率数据进行归一化处理,评估人员也可以使用这些比率对他们的 R 矩阵分析进行约束,这些 R 矩阵分析使用多组测量数据,并按照本工作中的建议进行了重新归一化处理。这种一致性保证了我们基于整个一致的 TOF 实验数据数据库对参考积分进行新评估的可靠性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Nuclear Data Sheets
Nuclear Data Sheets 物理-物理:核物理
CiteScore
7.80
自引率
5.40%
发文量
22
审稿时长
>12 weeks
期刊介绍: The Nuclear Data Sheets are current and are published monthly. They are devoted to compilation and evaluations of experimental and theoretical results in Nuclear Physics. The journal is mostly produced from Evaluated Nuclear Structure Data File (ENSDF), a computer file maintained by the US National Nuclear Data Center
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