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Lu Zou Sep. 12 th , 2005

What did I Learn in ’05 Summer? -- A report on Neutron and X-ray National School in Argonne National Laboratory. Lu Zou Sep. 12 th , 2005. Outline. Introduction to Neutron and X-Ray Scattering Introduction to APS and IPNS in Argonne National Lab

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Lu Zou Sep. 12 th , 2005

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  1. What did I Learn in ’05 Summer?-- A report on Neutron and X-ray National Schoolin Argonne National Laboratory Lu Zou Sep. 12th, 2005

  2. Outline • Introduction to Neutron and X-Ray Scattering • Introduction to APS and IPNS in Argonne National Lab • Neutron and X-Ray Detectors and Instrumentation • Neutron and X-Ray Experiments • Other Information

  3. 1895: Discovery of X-Ray Wilhelm Conrad Röntgen 1845-1923

  4. d 2 Scattering Geometry Incident Radiation (ki, Ei, pi) Scattered Radiation (kf, Ef, pf) Energy Transfer q = ki - kf ΔE = Ei – Ef

  5. Interaction Mechanisms

  6. Intrinsic Cross Section

  7. s æ ö d 2 = = ç b const. W d è ø 0 To “see ” 1H with Neutron diffraction, DEUTORATE ‘H’ to ‘D’

  8. Advanced Photon Source (APS) • e- Gun: Cathode ~1100 oC • LINAC • 450 MeV • >99.999% of C • Booster Synchrotron • 7 GeV • >99.999999% of C • Electron Storage Ring • 1104-m-circumference • > 1,000 electromagnets • Insertion Devices • Experiment Hall and Beamlines

  9. Intense Pulsed Neutron Source (IPNS) 50 MeV N P+ 450 MeV H- 750 keV 30 Hz

  10. X-Ray Detectors • Photons can only by “detected” by registering the deposition of energy in the detecting medium • Therefore, inelastic scattering processes (i.e. those that deposit energy) are relevant. • Photoelectric effect (Ionization Chambers) • Compton scattering (Scintillation Detectors) • Pair (e+, e-) production (Solid State Detectors)

  11. Neutron Detectors • To “detect” a neutron, one need to use nuclear reactions to “convert” neutros into charged particles (now, countable) • Then, use one of many types of charged particle detectors • Gas (3He) proportional counters and ionization chambers • Scintillation detectors (6Li) • Semiconductor detectors (6Li)

  12. X-Ray Instrumentation -- Mirror Index of Refraction Air (n1 ~ 1) R = [2/sin ] [F1 F2/(F1 + F2)] c n2 = 1 - - i c n2 2 Critical Angle for total External Reflection c = (2)1/2 Typical values for at 1Å is 10-5 to 10-6, so c is about 10-3 mrads.

  13. X-Ray Instrumentation -- Monochromators • Use Bragg’s Law to select a particular wavelength (or energy since  = hc/E), namely:  = 2d sin() • If we differentiate Bragg’s Law, we can determine the energy resolution of the monochromator.  /  = E/E = cot()   • Because of the small angular divergence of the x-ray beam in the vertical direction (and the polarization of the beam - in the plane of the orbit), synchrotron radiation monochromators normally diffract in the vertical plane.

  14. monochromatic polychromatic Double Crystal Monochronmators • The most common arrangement for a monochromator is the double-crystal monochromator. It: • is non-dispersive, that is all rays that diffract from the first crystal simultaneously diffract from the second crystal (if same crystals with same hkl’s are used) • keeps the beam fixed in space as the energy is changed.

  15. Neutron Instrumentation • Collimator • Monochromator • Analyzer • … I didn’t find enough information on this topic …

  16. Outline for 2nd part • Small Angle Scattering • Powder Diffraction • Reflectometry

  17. USAXS Small Angle Neutron and X-ray Scattering (SANS, SAXS) • Small Angle X-ray Scattering (SAXS) 0.06 <λ< 0.2 nm • Small Angle Neutron Scattering (SANS) 0.5 <λ< 2 nm • Small Angle Light Scattering (LS) 400 <λ< 700 nm

  18. Basic schematics of a SAS experiments

  19. kf·r Scattered beam P  2 |kf· r - ki· r| = Q · r  Q = |Q| = 4 sin ()  r Incident beam 2  O k = 2 ki·r Recall Bragg’s Lawλ=2dsinθ d = 2π/Q

  20. Guinier Plot • Look at scattering in low-Q regime • Plot the data as ln I(Q) vs Q2 • Needle shaped particles:I(Q) ~ Q-1 • Disk shaped particles:I(Q) ~ Q-2 • Spherical particles:I(Q) ~ Q-3

  21. Schultz Polydisperse Core Sherical Shell • “IGOR Pro. 5.03” • Debye Flexible Gaussian polymer • Solid Sphere • Schultz Polydisperse Sphere • Spherical Shell • … Sperical Shell

  22. Small angle scattering is used to study . . . • Polymer materials • Conformation of polymer molecules in solution and in bulk • Structure of microphase-separated block copolymers • Factors affecting miscibility of polymer blends • Biomaterials • Organization of biomolecular complexes in solution • Conformational changes affective function of proteins, enzymes, complexes, membranes, . . . • Pathways for protein folding • Chemistry • Colloidal suspensions, microemulsions, surfactant micelles • Molecular self-assembly in solution and on surfaces • Metals and ceramics • Deformation microstructures and precipitation

  23. Powder Diffraction • We don’t take a picture of atoms! • We live in a reciprocal space!

  24. 32-ID powder diffractometer – multi-analyzer/detector Parallel beam optics Analyzer • =0.49582Å (25keV) 2Q APS Detectors Sample (capillary) Beam optics l = 2dsinQ Vary 2Q

  25. 8 detectors used Beam pipe sample

  26. X-ray Powder Diffraction-- Mixture of Y2O3 and Al2O3 Software : EXPGUI By Dr. R.B. Von Dreele APS/IPNS Argonne National Laboratory Gaussian profile Lorentzian profile

  27. Summary for Powder Diffraction • Input Data • Powder scattering pattern data • Trial structure space group and approximate lattice parameters and atomic positions • Line shape function and Q-dependence of resolution • Output Results • Lattice Parameters • Refined atomic positions and occupancies • Thermal parameters for each atom site • Resolution parameters • Background parameters • R factors of fit • Preferential orientation, absorption, etc. • More than one phase can be separately refined

  28. Reflectometry

  29. Scattering Length Density (SLD) ρ(z) = Nb N = # of Atoms per unit volume b = Scattering length

  30. Reflectometry Applications • Polymer Interface • Magnetic superlattices and thin films • Langmuir-Blodgett filmes • Biological membranes • Electrochemistry • Superconductivity • Diffusion processes • … • Langmuir-Blodgett filmes • Interdiffusion • Surface and interfacial roughness • Structures • Biological membranes • Lipid layer structure • Protein adsorption

  31. Structural studies of Langmuir-Blodgett films • Dave Wiesler (NIST) • Lev Feigin (Moscow) • Wolfgang Knoll (Planck) • Albert Schmidt (Planck) • Mark Foster et. al. (Akron) • …

  32. Spallation Neutron Source (SNS)

  33. U.S. Neutron Scattering Schools 2006 School Topic: Soft Matter and Biological Materials • National Neutron and X-ray Scattering Summer School • Two weeks in August • http://www.dep.anl.gov/nx/ • Deadline  Apr.30 • NCNR-NIST Summer School • One week in June • http://www.ncnr.nist.gov/summerschool/index.html • Deadline  April • LANSCE Winter School in Neutron Scattering • Topic focus (changes each year) • 7-10 days in January • http://www.lansce.lanl.gov/neutronschool/; • Deadline  October

  34. How do we produce neutrons? • Fission • chain reaction • continuous flow • 1 neutron/fission • Spallation • no chain reaction • pulsed operation • 30 neutrons/proton

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