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Neutron scattering & disordered materials

Neutron scattering & disordered materials. Miguel A. González. Institut Laue Langevin (Grenoble, FRANCE). Neutrons: Low intensity ILL is for neutrons what a 6V bicycle lamp is for photons Expensive sources required (reactors, spallation sources).

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Neutron scattering & disordered materials

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  1. Neutron scattering & disordered materials Miguel A. González Institut Laue Langevin (Grenoble, FRANCE)

  2. Neutrons: Low intensity ILL is for neutrons what a 6V bicycle lamp is for photons Expensive sources required (reactors, spallation sources). Serious drawbacks: difficult to guide, focus, or detect. Not direct access (no laboratory facilities). We need really good reasons… and the properties of the neutron will give them all … Why neutrons?

  3. Subatomic particle (nucleon) Charge: zero Mass 1.0087 a.m.u. (1.675·10-27 kg) Spin of 1/2 h Magnetic moment µn = –1.9132 nuclear magneton = –9.65·10–27 J/T Basic properties of the neutron

  4. Neutron as a probe

  5. Neutron as a probe * Wavelength and energies well suited to explore interatomic distances and typical excitations in condensed matter (phonons, magnons, vibrational modes, ...)

  6. Neutron as a probe * Wavelength and energies well suited to explore interatomic distances and typical excitations in condensed matter (phonons, magnons, vibrational modes, ...) * Weak absorption: penetrates bulk of large samples & containers

  7. Neutron as a probe 1 10-2 Penetration deep (m) 10-4 10-6 10 20 30 40 60 70 80 90 0 50 Atomic number

  8. Neutron as a probe * Wavelength and energies well suited to explore interatomic distances and typical excitations in condensed matter (phonons, magnons, vibrational modes, ...) * Weak absorption: penetrates bulk of large samples & containers * Scattered (mainly) by nuclei: 1.Constant scattering length:Intensity at high scattering angles! 2. Arbitrarily changing with Z Light atoms beside heavy ones (H-O, Li-Mn, O-U) are visible Discriminating neighbours (O-N) 3. Arbitrarily changing with A:Isotopic exchange

  9. Neutron as a probe

  10. And very important ... Direct probe of the dynamic structure factor (or scattering law), which contains everything we want to know about the properties of the sample (both structure and dynamics)!

  11. What do we measure?

  12. Coherent and incoherent scattering coherent incoherent

  13. Information in both space and time H/D substitution and polymer dynamics

  14. The case of hydrogen 4b2 = 4b2 + 4(b2b2) total = coh + inc

  15. Dynamic structure factor S(Q,) is a correlation function related only to the properties of the scattering system. intermediate scattering function, I(Q,t) DIRECT RELATION: Measured quantity Physical information d2/dd S(Q, )

  16. More correlation functions S(Q,) is the Fourier transform in space and time of the density-density correlation function G(r,t): Van Hove time-dependent pair correlation function (1954)

  17. FT in time FT in space S(Q, )I(Q,t)G(r,t) [energy]1[][volume]1 Relations S(Q,), I(Q,t), G(r,t)

  18. D4C (ILL) • Large Q-range • High stability • High flux • Very low background • Simpler corrections

  19. Monoatomic system DQ Qp 3.8 Å P d FSDP First Sharp Diffraction Peak Liquid Ar @ 85K J.L. Yarnell et al. (1973) PRA 7, 2130 Fourier Transformation Limiting values  Normalisation

  20. What can we see with QENS & INS

  21. Self intermediate scattering function

  22. Kinds of instruments used

  23. Three-Axis Spectrometer (TAS) (Q,) explored in a step-by-step manner: 1. ki selected by Bragg reflection in a crystal monochromator (A1, A2) 2. Orientation of kf controlled by sample orientation (A3, A4) 3. kf selected by Bragg reflection in a crystal monochromator (A5, A6)

  24. Crystal-TOF spectrometer

  25. kf Q ki Kinematical range  Hot neutron spectrometer Cold neutron spectrometer

  26. SUMMARY - Neutron Scattering can provide unique information about the structure (isotopic substitution) and dynamics (simultaneous measurement of Q and ) of (disordered) matter. - Excellent complementary information to that provided by other techniques: dielectric spectroscopy, X-rays, NMR, ... And many possibilities to use neutrons around the world ...

  27. St Petersburg HMI Berlin Dubna FZ Jülich GKSS Kjeller Delft Isis Orphée Swierk ILL Grenoble Řez Prague FRM-II KFKI Budapest PSI Zurich Demokritis Athens Thank you and welcome!

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