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Clayton Anderson Neutron Scattering Phys 211A - Solid State Physics 1 17 December 2014

This article outlines the basic principles of neutron scattering in solid state physics, including elastic vs. inelastic scattering, coherent vs. incoherent scattering, neutron specific properties, penetration depth, and small cross sections. It also discusses the generation of the neutron beam and various applications of neutron scattering. Additionally, it explores magnetic neutron scattering and powdered neutron diffraction, and provides an example of the atomic structure of a high entropy alloy.

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Clayton Anderson Neutron Scattering Phys 211A - Solid State Physics 1 17 December 2014

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  1. Clayton Anderson Neutron Scattering Phys 211A - Solid State Physics 1 17 December 2014

  2. Outline Basic Principles - Scattering, Bragg’s law - Elastic vs. Inelastic - Coherent vs. Incoherent - Neutron specific properties - Penetration Depth - Small Cross Sections - Generating the beam Applications - “Generic” neutron scattering - Powdered neutron diffraction - Magnetic Scattering Atomic Structure of a HEA - What is a HEA? - Results

  3. Basic Principles • Neutrons do not have an electronic charge, so they scatter off nuclei instead of electron clouds. • Small probability of scattering • Penetration Depth • Scattering amplitude depends on neutron - nuclei interaction A beam of neutrons impinges on a sample, resulting in scattering. Scattering occurs for specific orientations of the crystal and specific wavelengths of the neutrons. This relationship is given by Bragg’s law:

  4. Marder, chapter 3 • Pynn, Chapter 2

  5. http://pd.chem.ucl.ac.uk/pdnn/inst3/neutrons.htm

  6. Generating the Beam • Spallation: high-energy protons impact on liquid mercury, ejecting neutrons. • Nuclear Fission Reactors: neutrons are generated by the decay of Uranium • n+235U −→236U −→92Kr+141Ba+ 3n How do we get neutrons?

  7. Oak Ridge National Laboratory • http://neutrons.ornl.gov/facilities/SNS/works.shtml

  8. Types of Scattering • Coherent elastic scattering is the “usual stuff.” • Coherent inelastic scattering yields information about the vibrations of the crystal (phonons). • Incoherent elastic scattering is noise. • Incoherent inelastic scattering provides information about atomic diffusion. Coherent Scattering - Interference between neutrons that scatter from different nuclei. Incoherent Scattering - Interference between neutrons that scatter from the same nuclei. Elastic Scattering - No energy is transferred upon collision Inelastic Scattering - Some energy is transferred upon collision

  9. Magnetic Neutron Scattering Neutron doesn’t have electronic charge, but it has a magnetic moment due to its quark composition. For magnetic scattering, only the component perpendicular to the scattering vector can impact the scattering.

  10. Powdered Neutron Scattering Neutron beam scatters off a powdered crystal sample, which includes all orientations of crystal planes. This results in rings corresponding to different atomic planes. • http://en.wikipedia.org/wiki/Powder_diffraction

  11. Example of actual data • HEA = High entropy alloy • Results of x-ray and neutron scattering lead show that ZrNbHf has an average b.c.c. structure, but is distorted towards f.c.c. • Guo,Local Atomic Structure

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