Neutron thermalization in nuclear graphite: A modern story of a classic moderator

Iyad I. Al-Qasir; Yongqiang Cheng; Jiao Y.Y. Lin; Anne A. Campbell; G. Sala; Kemal Ramic; Fahima F. Islam; Abdallah Qteish; Barry Marsden; Douglas L. Abernathy; Matthew B. Stone

doi:10.1016/j.anucene.2021.108437

Neutron thermalization in nuclear graphite: A modern story of a classic moderator

Iyad I. Al-Qasir, Yongqiang Cheng, Jiao Y.Y. Lin, Anne A. Campbell, G. Sala, Kemal Ramic, Fahima F. Islam, Abdallah Qteish, Barry Marsden, Douglas L. Abernathy, Matthew B. Stone

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Abstract

Graphite has been of great interest since the dawn of the nuclear era. In this work, we will focus on the thermal neutron scattering of two types of nuclear graphite that have different microstructures, namely, the historic PGA which has a very anisotropic medium-grained needle coke, and the new G347A which is a near-isotropic fine-grained graphite. We report the results of room temperature inelastic neutron scattering measurements for the scattering function, double differential scattering cross-section, and phonon density of states. The obtained results are discussed in conjunction with results extracted from first-principles lattice dynamics simulations of crystalline graphite, using the incoherent approximation and by also including the coherent-one phonon contribution. Excellent agreements have been found between the measured and calculated scattering functions and phonon densities of states. The inclusion of the coherent-one phonon scattering shows a significant improvement of the calculated scattering functions, double differentials, and inelastic scattering cross-sections. We also highlight the physical concerns about the current thermal neutron scattering ENDF/B-VIII of nuclear graphite library and its corresponding phonon density of states. This work aims to provide a new presentation of neutron thermalization by graphite and offers a new set of high quality experimental and computational data for consideration.

Original language	English
Article number	108437
Journal	Annals of Nuclear Energy
Volume	161
DOIs	https://doi.org/10.1016/j.anucene.2021.108437
State	Published - Oct 2021

Funding

The experimental material is based upon work that was conducted by I. I. Al-Qasir while a Visiting Research Fellow at the Shull Wollan Center- the University of Tennessee and Oak Ridge National Laboratory's Joint Institute for Neutron Sciences. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. I. I. Al-Qasir acknowledges the use of the HPC Facility at the University of Sharjah to perform the DFT simulations. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).

Funders	Funder number
Joint Institute for Neutron Sciences
U.S. Department of Energy
Office of Science
Oak Ridge National Laboratory
University of Tennessee
University of Sharjah

Keywords

ENDF/B-VIII
First-principles calculations
Nuclear graphite
Phonon density of states
Scattering function
Thermal neutron scattering

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10.1016/j.anucene.2021.108437

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title = "Neutron thermalization in nuclear graphite: A modern story of a classic moderator",

abstract = "Graphite has been of great interest since the dawn of the nuclear era. In this work, we will focus on the thermal neutron scattering of two types of nuclear graphite that have different microstructures, namely, the historic PGA which has a very anisotropic medium-grained needle coke, and the new G347A which is a near-isotropic fine-grained graphite. We report the results of room temperature inelastic neutron scattering measurements for the scattering function, double differential scattering cross-section, and phonon density of states. The obtained results are discussed in conjunction with results extracted from first-principles lattice dynamics simulations of crystalline graphite, using the incoherent approximation and by also including the coherent-one phonon contribution. Excellent agreements have been found between the measured and calculated scattering functions and phonon densities of states. The inclusion of the coherent-one phonon scattering shows a significant improvement of the calculated scattering functions, double differentials, and inelastic scattering cross-sections. We also highlight the physical concerns about the current thermal neutron scattering ENDF/B-VIII of nuclear graphite library and its corresponding phonon density of states. This work aims to provide a new presentation of neutron thermalization by graphite and offers a new set of high quality experimental and computational data for consideration.",

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author = "Al-Qasir, {Iyad I.} and Yongqiang Cheng and Lin, {Jiao Y.Y.} and Campbell, {Anne A.} and G. Sala and Kemal Ramic and Islam, {Fahima F.} and Abdallah Qteish and Barry Marsden and Abernathy, {Douglas L.} and Stone, {Matthew B.}",

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AU - Al-Qasir, Iyad I.

AU - Cheng, Yongqiang

AU - Lin, Jiao Y.Y.

AU - Campbell, Anne A.

AU - Sala, G.

AU - Ramic, Kemal

AU - Islam, Fahima F.

AU - Qteish, Abdallah

AU - Marsden, Barry

AU - Abernathy, Douglas L.

AU - Stone, Matthew B.

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AB - Graphite has been of great interest since the dawn of the nuclear era. In this work, we will focus on the thermal neutron scattering of two types of nuclear graphite that have different microstructures, namely, the historic PGA which has a very anisotropic medium-grained needle coke, and the new G347A which is a near-isotropic fine-grained graphite. We report the results of room temperature inelastic neutron scattering measurements for the scattering function, double differential scattering cross-section, and phonon density of states. The obtained results are discussed in conjunction with results extracted from first-principles lattice dynamics simulations of crystalline graphite, using the incoherent approximation and by also including the coherent-one phonon contribution. Excellent agreements have been found between the measured and calculated scattering functions and phonon densities of states. The inclusion of the coherent-one phonon scattering shows a significant improvement of the calculated scattering functions, double differentials, and inelastic scattering cross-sections. We also highlight the physical concerns about the current thermal neutron scattering ENDF/B-VIII of nuclear graphite library and its corresponding phonon density of states. This work aims to provide a new presentation of neutron thermalization by graphite and offers a new set of high quality experimental and computational data for consideration.

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Neutron thermalization in nuclear graphite: A modern story of a classic moderator

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