[en] Highlights: • Performed double differential scattering cross section measurements for polyethylene. • Measured dynamic structure factor for polyethylene at VISION spectrometer. • Developed a new methodology for creation of thermal scattering libraries. • Produced a new improved thermal scattering library for polyethylene. - Abstract: Improvements in determination of the thermal scattering law of moderator materials (measuring, calculating and validating) are important for accurate prediction of neutron thermalization in nuclear systems. In this work a methodology for producing thermal scattering libraries from the experimental data for polyethylene (C2H4)n is discussed. Double differential scattering cross section (DDSCS) experiments were performed at the Spallation Neutron Source of Oak Ridge National Laboratory (SNS ORNL). New scattering kernel evaluations, based on phonon spectrum for (C2H4)n, are created using the NJOY2016 code. Two different methods were used: direct and indirect geometry neutron scattering at ARCS and SEQUOIA, and VISION instruments, respectively, where the phonon spectrum was derived from the dynamical structure factor S(Q,ω) obtained from the measured DDSCS. In order to compare and validate the newly created library, the experimental setup was simulated using MCNP6.1. Compared with the current ENDF/B-VII.1, the resulting RPI (C2H4)n libraries improved both double differential scattering and total scattering cross sections. A set of criticality benchmarks containing (C2H4)n from HEU-MET-THERM resulted in an overall improved calculation of Keff, although the libraries should be tested against benchmarks more sensitive to (C2H4)n. The DFT + oClimax method is used and is shown to be most comprehensive method for analysis of moderator materials. The importance of DFT + oClimax method lies in the fact that it can be validated against all data measured at VISION, ARCS and SEQUOIA, and experimental total scattering cross section measurements.
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[en] Highlights: • Performed double differential scattering cross section measurements for lucite. • Measured dynamic structure factor for lucite at VISION spectrometer. • Developed a new methodology for creation of thermal scattering libraries. • Produced a new improved thermal scattering library for lucite. - Abstract: With the advancements in technology (both experimental and computational) the determination of the“true” experimental phonon spectrum became more accessible. In this work a methodology for producing thermal scattering libraries from the experimental data (namely the DFT + oClimax method) for lucite (C5O2H8)n is discussed. Double differential scattering cross section (DDSCS) experiments were performed at the Spallation Neutron Source of Oak Ridge National Laboratory (SNS ORNL). New scattering kernel evaluations, based on the phonon spectrum for (C5O2H8)n,were created using oClimax and NJOY2016 codes. In order to compare and asses the performance of the newly created library, the experimental setup was simulated using MCNP6.1. Compared to the current ENDF/B-VIII.0, the resulting RPI (C5O2H8)n library improved the calculation of both double differential scattering and total scattering cross sections. A set of criticality benchmarks containing (C5O2H8)n from HEU-MET-THERM resulted in an overall improved calculation of . The DFT + oClimax method is shown to be the most comprehensive method for analysis of moderator materials, due to the fact that it can be verified against all data measured at VISION, ARCS and SEQUOIA neutron spectrometers at SNS ORNL, and experimental total scattering cross section measurements. This method also provides a new technique for calculating any phonon spectrum-related quantities such as scattering law kernel, specific heat capacity, thermal conductivity, etc. for any solid state material.
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