On a measurement approach to support evaluation of thermal scattering law data

Journal Article · Tue Jul 30 00:00:00 EDT 2019 · Annals of Nuclear Energy

DOI:https://doi.org/10.1016/j.anucene.2019.106940· OSTI ID:1848122

Hawari, Ayman I. ^[1]

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1. North Carolina State Univ., Raleigh, NC (United States)

Inelastic thermal neutron scattering in materials that act as neutron moderators, reflectors, and filters results in shaping the neutron spectrum at low energies. This phenomenon is described using differential scattering cross sections calculated from three components including the bound atom (i.e., nuclear) scattering cross section of the neutron, the ratio of the outgoing and incoming neutron energy, and the thermal scattering law (TSL), i.e., S(α,β), where α and β represent dimensionless momentum and energy exchange variables, respectively. To date, no TSL libraries are generated using measured data. However, valuable information may be derived from measurements and “targeted” experiments that can validate TSL data and the related inelastic scattering cross sections. As a demonstration, a suite of coordinated measurements and experiments is described that was designed and used to support the evaluation of the TSL for “nuclear” graphite. This experimental suite includes neutron powder diffraction (for structure analysis), positron annihilation (for nano porosity assessment), inelastic neutron scattering measurements using a chopper spectrometer, transmission experiments using neutrons with energy below the Bragg cutoff thereby accessing the total (inelastic) cross section, and a slowing-downtime experiment to observe the developing neutron spectrum in the material. We find that this experimental suite was key to understanding the difference in TSL between “nuclear” and “ideal” graphite and for the inclusion of “nuclear” graphite in the ENDF/B-VIII.0 nuclear data library release.

• Research Organization: North Carolina State University, Raleigh, NC (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE); USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); The US Naval Nuclear Propulsion Program (NNPP)
• Grant/Contract Number: NE0008444
• OSTI ID: 1848122
• Alternate ID(s): OSTI ID: 1563038
• Journal Information: Annals of Nuclear Energy, Vol. 135, Issue C; ISSN 0306-4549
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
Nuclear Criticality Safety Program (NCSP)
Nuclear Science & Technology
Neutron
Thermal Scattering Law
Cross Section
Measurement
ENDF