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Why Diffraction, Why Neutrons?

Why Diffraction, Why Neutrons?. J. A. Dura dura@nist.gov. NCNR Summer School on. Neutron Small Angle Scattering and Reflectometry. June 26, 2006. Why Diffraction?. 3 choices for microscopic structural information. Neutron Energy, Momentum, and Wavelength. A Neutron Scattering Instrument:

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Why Diffraction, Why Neutrons?

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  1. Why Diffraction, Why Neutrons? J. A. Dura dura@nist.gov NCNR Summer School on Neutron Small Angle Scattering and Reflectometry June 26, 2006

  2. Why Diffraction? 3 choices for microscopic structural information

  3. Neutron Energy, Momentum, and Wavelength

  4. A Neutron Scattering Instrument: • Creates a beam with a well defined • Measures the amount of scattered neutrons into a well defined • Thereby probes various Q or “Scans” Reciprocal space to determine S( Q ) Scattering Events and Reciprocal Space

  5. Scattering Function S( ,w) S( )=0 S( )>0 Destructive Interference • Im=I0 * S( ,w) • Depends only on sample/independent of instrument • Each point in reciprocal space derived from entire sample • Representative sampling of whole Reciprocal space needed • to fully recreate sample Constructive Interference

  6. Why Neutrons? The properties of the neutron lead to unique experimental techniques with particular advantages Neutron Interactions and Dosimetry Group / Physics Laboratory • Subatomic Particle • Particle & Related Physics • Nuclear Activation • PGAA, NDP, Radiography • Energies ~excitations in materials • Inelastic Scattering PGAA NDP Cold Neutron Trap

  7. Elastic vs. Inelastic Scattering Probes dynamics: energy transferred from excitations in the sample Probes structures by interference of neutrons scattered from them

  8. Why Neutrons? The properties of the neutron lead to unique experimental techniques with particular advantages • Spin 1/2 Particle • magnetic sensitivity • Neutral Particle -Interacts with • Nucleus via Strong Force • light element sensitivity (independent of Z) • isotope effect • isotropic scattering (no form factor) • Subatomic Particle • Particle & Related Physics • Nuclear Activation • PGAA, NDP, Radiography • Energies ~excitations in materials • Inelastic Scattering • Wavelength~ atomic spacing lower limit on sizes • Geometry of the motions • Interferometry • Elastic Scattering Techniques • (SANS, NR, Diffraction) Nuclear Magnetic

  9. Why Neutrons? The properties of the neutron lead to unique experimental techniques with particular advantages • Spin 1/2 Particle • magnetic sensitivity • Neutral Particle -Interacts with • Nucleus via Strong Force • light element sensitivity (independent of Z) • isotope effect • isotropic scattering (no form factor) • Neutral Particle –Weakly interacting • & penetrating • Simplified scattering theory • Non-destructive • Simplified sample environments • Penetrates the whole sample • Imaging • Residual Stress Analysis • Probes the entire sample simultaneously • Statistics on sample wide distributions of features • Subatomic Particle • Particle & Related Physics • Nuclear Activation • PGAA, NDP, Radiography • Energies ~excitations in materials • Inelastic Scattering • Wavelength~ atomic spacing lower limit on sizes • Geometry of the motions • Interferometry • Elastic Scattering Techniques • (SANS, NR, Diffraction)

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