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 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 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 22 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
7 To “see ” 1 H with Neutron diffraction, DEUTORATE ‘H’ to ‘D’ const. d d 2 0 b
8 Advanced Photon Source (APS) e - Gun: Cathode ~1100 o C 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
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 ( 3 He) proportional counters and ionization chambers –Scintillation detectors ( 6 Li) –Semiconductor detectors ( 6 Li)
12 X-Ray Instrumentation -- Mirror cc Air ( n 1 ~ 1) 22 n2n2 cc Critical Angle for total External Reflection c = (2 ) 1/2 n 2 = 1 - - i Index of Refraction Typical values for at 1Å is 10 -5 to 10 -6, so c is about 10 -3 mrads. R = [2/sin ] [F1 F2/(F1 + F2)]
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 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 Neutron Instrumentation Collimator Monochromator Analyzer … I didn’t find enough information on this topic …
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 Powder Diffraction We don’t take a picture of atoms! We live in a reciprocal space!
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 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
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 Fission chain reaction continuous flow 1 neutron/fissionSpallation no chain reaction pulsed operation 30 neutrons/proton How do we produce neutrons?