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Introduction to Quasi-Elastic Neutron Scattering (QENS). Presented to National School on Neutron and X-ray Scattering Ken Herwig Deputy Director Neutron Scattering Science Division, Oak Ridge National Laboratory September 29, 2008. OUTLINE. Background Neutrons and QENS
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Presented toNational School on Neutron and X-ray Scattering
Ken HerwigDeputy Director
Neutron Scattering Science Division, Oak Ridge National Laboratory
September 29, 2008
57Neutrons, QENS, and the Large Incoherent Cross-section of H
1,3 diphenylpropane tethered to the pore surface of MCM-41
Lattice and Spin Excitations
Small Molecule Diffusion
Large Scale Motions
Polymers and Biological Systems
Ultracold Neutrons Fundamental Physics
ARCS Fermi Chopper
SEQUOIA Fermi Chopper
Cold Neutron Chopper Spectrometer
Neutron Spin EchoThe SNS Inelastic Instrument Suite
Motions Too Fast for HFBS
TM = 277 K
Volino and Dianoux, Mol. Phys. 41, 271-279 (1980).
-> restricted motion
The transmission, T, depends on sample thickness, t, as:
Rotational Correlation Time
Radius of Gyration
Translational Diffusion Constant
Mean Jump Distance
Courtesy of Florian Kargl
SiO2 + Na2O, K2O, Al2O3, Fe2O3, CaO, MgO ...
effusive (flow) or explosive (fragmentation) eruption:
– H2O content in magma chamber (up to ≈15 mole%)
– viscosity of the anhydrous silicate melt (composition)
fast sodium relaxation on picosecond time scale
=> sodium diffusion (IN5)
Si-O network relaxation on nanosecond time scale
=> viscous flow (HFBS)
A. Meyer, H. Schober, D. B. Dingwell, Europhys. Lett. 59, 708 (2002)
Spider dragline silk possesses outstanding mechanical properties. It is spun at ambient temperature and pressure using water as a solvent. It is therefore crucial to understand the role of adsorbed water to spider silk.
T. Seydel, M. Koza, D. Sapede, C. Riekel, T. Forsyth, F. Vollrath, ILL annual report, 58 (2003).
The mobility of the polymer chains is enhanced by the presence of water.
D. Sapede, T. Seydel, V.T. Forsyth, M.M. Koza, R. Schweins,
F. Vollrath, and C. Riekel, Macromolecules 38, 8447 (2005).
Data from IN16