ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Division Spotlight
Radiation Protection & Shielding
The Radiation Protection and Shielding Division is developing and promoting radiation protection and shielding aspects of nuclear science and technology — including interaction of nuclear radiation with materials and biological systems, instruments and techniques for the measurement of nuclear radiation fields, and radiation shield design and evaluation.
Meeting Spotlight
ANS Student Conference 2025
April 3–5, 2025
Albuquerque, NM|The University of New Mexico
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
Latest Magazine Issues
Mar 2025
Jul 2024
Latest Journal Issues
Nuclear Science and Engineering
March 2025
Nuclear Technology
Fusion Science and Technology
February 2025
Latest News
Molten salt research is focus of ANS local section presentation
The American Nuclear Society’s Chicago–Great Lakes Local Section hosted a presentation on February 27 on developments at the molten salt research reactor at Abilene Christian University’s Nuclear Energy Experimental Testing (NEXT) Lab.
A recording of the presentation is available on the ANS website.
N. F. Wikner, G. D. Joanou, D. E. Parks
Nuclear Science and Engineering | Volume 19 | Number 1 | May 1964 | Pages 108-129
Technical Paper | doi.org/10.13182/NSE64-A19795
Articles are hosted by Taylor and Francis Online.
In this work our ability to understand thermal-neutron spectra in graphite-moderated reactor systems is examined on the basis of a theoretical description of neutron scattering that begins at the microscopic level. The first step in this examination consists in determining the extent to which current ideas of lattice vibrations in graphite are consistent with measurements of the scattering law and of specific heats. Theoretical scattering laws and specific heats based on a few different models for lattice vibrations are compared with experimental results. The theoretical scattering law is calculated within the framework of the incoherent and Gaussian approximations. The question of the accuracy of the latter approximation is discussed in detail. No estimates have been made of the magnitude of the uncertainty introduced by the use of the incoherent approximation. Following the discussion of neutron scattering at the microscopic level, we show (1) the sensitivity of various integral properties of the scattering kernel and of thermal-neutron spectra in a homogeneous medium to the frequency distribution of lattice vibrations, and (2) the accuracy of the Gaussian approximation for use in computing thermal-neutron spectra in graphite. Finally, a detailed theoretical model for the scattering of neutrons by graphite is applied to the problem of comparing calculated neutron spectra with the measured spectra in two strongly heterogeneous, graphite-moderated assemblies. These considerations show that current theoretical ideas concerning the frequency distribution of lattice vibrations in graphite are consistent with the results of the measurement of the scattering law, with the specific heat, and with most of the available results of the measurements of thermal-neutron spectra in reactor-like configurations.