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Methodology for Generating Covariance Data of Thermal Neutron Scattering Cross Sections
Nuclear Science and Engineering ( IF 1.2 ) Pub Date : 2020-09-08 , DOI: 10.1080/00295639.2020.1792716
Chris W. Chapman 1 , Goran Arbanas 1 , Alexander I. Kolesnikov 2 , Luiz Leal 3 , Yaron Danon 4 , Carl Wendorff 4 , Kemal Ramić 4 , Li Liu 4 , Farzad Rahnema 5
Affiliation  

Abstract This paper details and implements a framework for evaluating thermal neutron scattering cross sections that provide data and covariance data for hydrogen in light water. This methodology involves perturbing model parameters of molecular dynamics potentials and fitting the simulation results to experimental data. The framework is general and can be applied to any material or simulation method. The fit is made using the Unified Monte Carlo method to experimentally measure double-differential scattering cross sections of light water at the Spallation Neutron Source at Oak Ridge National Laboratory. Mean values and covariance data were generated for model parameters, phonon density of states, double-differential cross sections, and total scattering cross sections. These posterior parameter values were very similar to their prior values with a maximum relative error of 0.54%. This falls within in the Unified Monte Carlo–calculated uncertainties on the order of 2.7%. Additionally, posterior double-differential cross sections agree favorably with ENDF/B-VIII.0 cross sections. The new thermal scattering law was tested by comparing it against benchmarks from the International Criticality Safety Benchmark Evaluation Project Handbook, which showed a slight improvement over the ENDF/B-VIII.0 library. Additionally, the covariance matrix of the phonon density of states was validated to confirm that the spread of keff from the density of states used to generate the covariance matrix was similar to the spread of keff from the density of states of the sampled covariance matrix.

中文翻译:

生成热中子散射截面协方差数据的方法

摘要 本文详细介绍并实现了一个评估热中子散射截面的框架,该框架提供了轻水中氢的数据和协方差数据。该方法涉及扰动分子动力学势的模型参数并将模拟结果与实验数据拟合。该框架是通用的,可以应用于任何材料或模拟方法。拟合是使用统一蒙特卡罗方法在橡树岭国家实验室的散裂中子源处通过实验测量轻水的双微分散射截面进行的。为模型参数、声子状态密度、双微分截面和总散射截面生成平均值和协方差数据。这些后验参数值与它们的先前值非常相似,最大相对误差为 0.54%。这属于统一蒙特卡罗计算的 2.7% 的不确定性。此外,后双差分横截面与 ENDF/B-VIII.0 横截面一致。通过将新的热散射定律与国际临界安全基准评估项目手册中的基准进行比较,对新的热散射定律进行了测试,该手册显示比 ENDF/B-VIII.0 库略有改进。此外,验证了声子状态密度的协方差矩阵,以确认用于生成协方差矩阵的状态密度的 keff 扩展类似于采样协方差矩阵的状态密度的 keff 扩展。这属于统一蒙特卡罗计算的 2.7% 的不确定性。此外,后双差分横截面与 ENDF/B-VIII.0 横截面一致。通过将新的热散射定律与国际临界安全基准评估项目手册中的基准进行比较,对新的热散射定律进行了测试,该手册显示比 ENDF/B-VIII.0 库略有改进。此外,验证了声子状态密度的协方差矩阵,以确认用于生成协方差矩阵的状态密度的 keff 扩展类似于采样协方差矩阵的状态密度的 keff 扩展。这属于统一蒙特卡罗计算的 2.7% 的不确定性。此外,后双差分横截面与 ENDF/B-VIII.0 横截面一致。通过将新的热散射定律与国际临界安全基准评估项目手册中的基准进行比较,对新的热散射定律进行了测试,该手册显示比 ENDF/B-VIII.0 库略有改进。此外,验证了声子状态密度的协方差矩阵,以确认用于生成协方差矩阵的状态密度的 keff 扩展类似于采样协方差矩阵的状态密度的 keff 扩展。后双差分横截面与 ENDF/B-VIII.0 横截面一致。通过将新的热散射定律与国际临界安全基准评估项目手册中的基准进行比较,对新的热散射定律进行了测试,该手册显示比 ENDF/B-VIII.0 库略有改进。此外,验证了声子状态密度的协方差矩阵,以确认用于生成协方差矩阵的状态密度的 keff 扩展类似于采样协方差矩阵的状态密度的 keff 扩展。后双差分横截面与 ENDF/B-VIII.0 横截面一致。通过将新的热散射定律与国际临界安全基准评估项目手册中的基准进行比较,对新的热散射定律进行了测试,该手册显示比 ENDF/B-VIII.0 库略有改进。此外,验证了声子状态密度的协方差矩阵,以确认用于生成协方差矩阵的状态密度的 keff 扩展类似于采样协方差矩阵的状态密度的 keff 扩展。
更新日期:2020-09-08
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