Chapter

Chapter 6.1 Intensity of diffracted intensities

Mathematical, physical and chemical tables

First Online Edition (2006)

Part 6. Interpretation of diffracted intensities

  1. P. J. Brown1,
  2. A. G. Fox2,
  3. E. N. Maslen3,
  4. M. A. O’Keefe4,
  5. B. T. M. Willis5

Published Online: 1 JAN 2006

DOI: 10.1107/97809553602060000600

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Brown, P. J., Fox, A. G., Maslen, E. N., O’Keefe, M. A. and Willis, B. T. M. 2006. Intensity of diffracted intensities. International Tables for Crystallography. C:6:6.1:554–595.

Author Information

  1. 1

    Institut Laue–Langevin, Avenue des Martyrs, BP 156X, F‐38042 Grenoble CEDEX, France

  2. 2

    Center for Materials Science and Engineering, Naval Postgraduate School, Monterey, CA 93943‐5000, USA

  3. 3

    Crystallography Centre, The University of Western Australia, Nedlands, Western Australia 6009, Australia

  4. 4

    National Center for Electron Microscopy, Lawrence Berkeley National Laboratory MS‐72, University of California, Berkeley, CA 94720, USA

  5. 5

    Chemical Crystallography Laboratory, University of Oxford, 9 Parks Road, Oxford OX1 3PD, England

Publication History

  1. Published Online: 1 JAN 2006

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Abstract

Section 6.1.1 covers X‐ray scattering from atoms and ions. Scattering is described by the Thomson formula, including coherent (Rayleigh) and incoherent (Compton) X‐ray scattering. Atomic scattering factors, calculated using relativistic Hartree–Fock or Dirac–Slater wavefunctions, give the X‐ray scattering from an atom (in fact, its ensemble of electrons) in terms of that from a single electron. Free‐atom scattering factors are tabulated for neutral atoms from atomic number 1 (hydrogen) to 98 (californium) over a scattering range of sin θ/λ from 0 to 6 Å−1, and for ions from H1− to Pu6+ over 0 to 2 Å−1. Analytical fits to the scattering factors are given and methods for interpolation of the tabulated factors are described. Perturbations from free‐atom electron density for bound atoms are handled with generalized scattering factors expressed as spherical harmonics. Probability density functions for atom displacement due to temperature are described in terms of generalized temperature factors related to atom vibration symmetries. The final parts of Section 6.1.1 describe the role of atomic scattering factors in the computation of crystal structure factors by summation over unit‐cell atoms, and the reflecting power of small crystals. Section 6.1.2 presents the basic equations governing magnetic scattering of neutrons. They are used to define the useful intermediate quantities of the magnetic interaction vector, the magnetic structure factor and the magnetic form factor, which are used in calculations of magnetic cross sections. A brief account of the way in which the magnetic scattering depends upon the neutron spin direction (neutron polarization) is included. Formulae for the scattering of neutrons by the nuclei of an atom are given in Section 6.1.3. The scattering cross sections for a single nucleus, for an element containing a mixture of isotopes, and for a single crystal are considered.

Keywords:

  • approximations;
  • atomic scattering factors;
  • coherent scattering;
  • Compton scattering;
  • cumulant expansion;
  • curvilinear density functions;
  • Fourier‐invariant expansions;
  • Gram–Charlier series expansion;
  • incoherent scattering;
  • magnetic form factors;
  • magnetic scattering;
  • magnetic structure factors;
  • neutron polarization;
  • neutron scattering;
  • neutrons;
  • nuclear scattering;
  • polarization;
  • polarized neutrons;
  • quasi‐Gaussian approximation;
  • Rayleigh scattering;
  • reflecting power;
  • scattering;
  • scattering factors;
  • structure factors;
  • X‐ray scattering