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1 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.

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Presentation on theme: "1 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."— Presentation transcript:

1 1 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

2 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 3 1895: Discovery of X-Ray Wilhelm Conrad Röntgen

4 4 d  22 Scattering Geometry Incident Radiation (k i, E i, p i ) Scattered Radiation (k f, E f, p f ) Energy Transfer q = k i - k f ΔE = E i – E f

5 5 Interaction Mechanisms

6 6 Intrinsic Cross Section

7 7 To “see ” 1 H with Neutron diffraction, DEUTORATE ‘H’ to ‘D’ const. d d 2 0        b 

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

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

10 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 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 ( 3 He) proportional counters and ionization chambers –Scintillation detectors ( 6 Li) –Semiconductor detectors ( 6 Li)

12 12 X-Ray Instrumentation -- Mirror cc Air ( n 1 ~ 1) 22 n2n2 cc Critical Angle for total External Reflection  c = (2  ) 1/2 n 2 = 1 -  - i  Index of Refraction Typical values for  at 1Å is to 10 -6, so  c is about mrads. R = [2/sin  ] [F1 F2/(F1 + F2)]

13 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 14 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. polychromatic monochromatic

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

16 16

17 17 Outline for 2 nd part Small Angle Scattering Powder Diffraction Reflectometry

18 18 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 USAXS

19 19 Basic schematics of a SAS experiments

20 20 Incident beam Scattered beam P O ki·rki·r kf·rkf·r 2  |k f · r - k i · r| = Q · r Q = |Q| = 4  sin (  ) 22 r k = 2  Recall Bragg’s Law λ=2dsinθ d = 2π/Q

21 21 Guinier Plot Look at scattering in low-Q regime Plot the data as ln I(Q) vs Q 2 Needle shaped particles: I(Q) ~ Q -1 Disk shaped particles: I(Q) ~ Q -2 Spherical particles: I(Q) ~ Q -3

22 22 “IGOR Pro. 5.03” Debye Flexible Gaussian polymer Solid Sphere Schultz Polydisperse Sphere Spherical Shell … Sperical Shell Schultz Polydisperse Core Sherical Shell

23 23 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

24 24 Powder Diffraction We don’t take a picture of atoms! We live in a reciprocal space!

25 25

26 26

27 27 Sample (capillary) Detectors  Å (25keV) 22 APS Analyzer Beam optics = 2dsin  Vary 2  Parallel beam optics 32-ID powder diffractometer – multi-analyzer/detector

28 28 8 detectors used sample Beam pipe

29 29 X-ray Powder Diffraction -- Mixture of Y 2 O 3 and Al 2 O 3 Software : EXPGUI By Dr. R.B. Von Dreele APS/IPNS Argonne National Laboratory Gaussian profile Lorentzian profile

30 30 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

31 31 Reflectometry

32 32 Scattering Length Density (SLD) ρ( z ) = Nb N = # of Atoms per unit volume b = Scattering length

33 33

34 34 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

35 35 Structural studies of Langmuir-Blodgett films Dave Wiesler (NIST) Lev Feigin (Moscow) Wolfgang Knoll (Planck) Albert Schmidt (Planck) Mark Foster et. al. (Akron) …

36 36 Spallation Neutron Source (SNS)

37 37 U.S. Neutron Scattering Schools National Neutron and X-ray Scattering Summer School –Two weeks in August –http://www.dep.anl.gov/nx/http://www.dep.anl.gov/nx/ –Deadline  Apr.30 NCNR-NIST Summer School –One week in June –http://www.ncnr.nist.gov/summerschool/index.htmlhttp://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/;http://www.lansce.lanl.gov/neutronschool/ –Deadline  October

38 38 Fission chain reaction continuous flow 1 neutron/fissionSpallation no chain reaction pulsed operation 30 neutrons/proton How do we produce neutrons?


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