Introduction to Neutron ScatteringWhy Neutrons?Neutrons vs. X-rays!How are neutrons useful?How do we get neutrons? Research Reactor SourcesHow do we get neutrons? Spallation SourcesHow do we get neutrons? Reactor or Spallation SourcesWhere can you find neutron sources?What is neutron scattering?The Neutron Scattering FactorElastic Neutron ScatteringInelastic Neutron ScatteringVibrational and Magnetic ExcitationsInelastic Neutron Scattering: A magnetic example!SummaryIntroduction to Neutron ScatteringJason T. HaraldsenAdvanced Solid State II2/27/2007Why Neutrons?Neutrons have No Charge!• Highly penetrating• Nondestructive• Can be used in extremesNeutrons have a Magnetic Moment!• Magnetic structure• Fluctuations• Magnetic materialsNeutrons have Spin!• Polarized beams• Atomic orientation• Coherent and incoherent scatteringThe Energies of neutrons are similar to the energies of elementary excitations!• Molecular Vibrations and Lattice modes• Magnetic excitationsThe Wavelengths of neutrons are similar to atomic spacing!• Sensitive to structure• Gathers information from 10-10 to 10-7 m• Crystal structures and atomic spacingsNeutrons probe Nuclei!• Light atom sensitive• Sensitive to isotopic substitutionNeutrons vs. X-rays!Neutrons allow easy access to atoms that are usually unseen in X-ray ScatteringChatterji, Neutron Scattering from Magnetic Materials (2006)How are neutrons useful?Mitchell et. al, Vibrational Spectroscopy with Neutrons (2005)How do we get neutrons?Research Reactor SourcesUses nuclear fission to create neutronsContinuous neutron fluxFlux is dependent on fission rateLimited by heat flow in from the reaction Creates radioactive nuclear wastePynn, Neutron Scattering: A Primer (1989)How do we get neutrons?Spallation SourcesUses a cascade effect from the collision of a proton on a heavy metal.Pulsed SourceHigh IntensityHeat production is relatively lowMitchell et. al, Vibrational Spectroscopy with Neutrons (2005)How do we get neutrons?Reactor or Spallation SourcesSpallation SourcesPulsed sourceHigh intensityHeat production is relatively lowReactor SourcesContinuous fluxLimited by heat flow in from the reaction Mitchell et. al, Vibrational Spectroscopy with Neutrons (2005)Where can you find neutron sources?www. ornl.govWhat is neutron scattering?Elastic Neutron ScatteringNo loss of energyExamines the change in momentum or angle of the neutrons.Inelastic Neutron ScatteringExamines both momentum and energy dependencies.Pynn, Neutron Scattering: A Primer (1989)The Neutron Scattering FactorNeutron Structure FactorPair Correlation FunctionFourier TransformSquires, Introduction to the theory of thermal neutron scattering (1996)Total Differential Cross-SectionElastic Neutron ScatteringDetermine length scales and differentiate between nano-, micro-, and macro-systems.Utilizes position and momentum correlation.Mitchell et. al, Vibrational Spectroscopy with Neutrons (2005)Pynn, Neutron Scattering: A Primer (1989)Inelastic Neutron ScatteringUses both change in momentum and energy to characterize a systems vibrational, magnetic, and lattice excitations.Mitchell et. al, Vibrational Spectroscopy with Neutrons (2005)Vibrational and Magnetic Excitations•Vibrational excitations are broad, large excitations.Neutrons observe all phonon and vibrational excitations. The intensity is determined by the phonons polarization vectors.•Magnetic excitations are detailed by spin transitions of ΔS = 0 and ± 1.Q-dependence of magnetic excitations help determine the magnetic structure within the material.Magnetic Excitations Phonon ExcitationsM. B. Stone et al. Unpublished (2007)Inelastic Neutron Scattering:A magnetic example!The use of neutron scattering on the material of VODPO4 ● ½ D2O clarified the magnetic structure of the material.Tennant et. al, PRL (1997)V4+V4+V4+SummaryNeutrons are produced in two main waysResearch ReactorsSpallation SourcesUtilizes the properties of the neutron.Neutrons are useful in determining not only structural properties of a material, but also the vibrational, magnetic, and lattice