# Difference between revisions of "Atomic scattering factor"

### From Online Dictionary of Crystallography

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BrianMcMahon (talk | contribs) (Tidied translations and added German (U. Mueller)) |
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− | < | + | <font color="blue">Facteur de diffusion atomique</font> (''Fr''). <font color="red">Atomformfaktor, Formfaktor</font> (''Ge''). <font color="black">Fattore di diffusione atomico</font> (''It''). <font color="purple">原子散乱因子</font> (''Ja''). <font color="green">Factor de forma atómica</font> (''Sp''). |

== Definition == | == Definition == | ||

− | A measure of the scattering power of an isolated atom. Also known as the '''atomic form factor'''. The scattering factor depends on the scattering amplitude of an individual atom | + | A measure of the scattering power of an isolated atom. Also known as the '''atomic form factor'''. The scattering factor depends on the scattering amplitude of an individual atom, on the [[Bragg angle]] and the type of radiation involved. |

== X-ray scattering == | == X-ray scattering == | ||

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The scattering amplitude from a neutral atom depends on the number of electrons (''Z'' = the atomic number) and also on the [[Bragg angle]] θ – destructive interference among waves scattered from the individual electrons reduces the intensity at other than zero scattering angle. For θ = 0 the scattering amplitude is normally equal to ''Z''. However, the scattering factor is modified by [[anomalous scattering]] if the incident wavelength is near an absorption edge of the scattering element. | The scattering amplitude from a neutral atom depends on the number of electrons (''Z'' = the atomic number) and also on the [[Bragg angle]] θ – destructive interference among waves scattered from the individual electrons reduces the intensity at other than zero scattering angle. For θ = 0 the scattering amplitude is normally equal to ''Z''. However, the scattering factor is modified by [[anomalous scattering]] if the incident wavelength is near an absorption edge of the scattering element. | ||

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The X-ray scattering factor is evaluated as the Fourier transform of the electron density distribution of an atom or ion, which is calculated from theoretical wavefunctions for free atoms. | The X-ray scattering factor is evaluated as the Fourier transform of the electron density distribution of an atom or ion, which is calculated from theoretical wavefunctions for free atoms. | ||

− | == | + | == References == |

− | Electron diffraction | + | *''Electron diffraction'': C. Colliex, J. M. Cowley, S. L. Dudarev, M. Fink, J. Gjønnes, R. Hilderbrandt, A. Howie, D. F. Lynch, L. M. Peng, G. Ren, A. W. Ross, V. H. Smith Jr, J. C. H. Spence, J. W. Steeds, J. Wang, M. J. Whelan and B. B. Zvyagin. ''International Tables for Crystallography'' (2006). Vol. C, ch. 4.3, pp. 259-429 [http://dx.doi.org/10.1107/97809553602060000593 doi:10.1107/97809553602060000593] |

− | C. Colliex, J. M. Cowley, S. L. Dudarev, M. Fink, J. Gjønnes, R. Hilderbrandt, A. Howie, D. F. Lynch, L. M. Peng, G. Ren, A. W. Ross, V. H. Smith Jr, J. C. H. Spence, J. W. Steeds, J. Wang, M. J. Whelan and B. B. Zvyagin. ''International Tables for Crystallography'' (2006). Vol. C, ch. 4.3, pp. 259-429 [http://dx.doi.org/10.1107/97809553602060000593 doi:10.1107/97809553602060000593] | + | *''Intensity of diffracted intensities'': P. J. Brown, A. G. Fox, E. N. Maslen, M. A. O'Keefe and B. T. M. Willis. ''International Tables for Crystallography'' (2006). Vol. C, ch. 6.1, pp. 554-595 [http://dx.doi.org/10.1107/97809553602060000600 doi:10.1107/97809553602060000600] |

+ | *''Neutron techniques'': I. S. Anderson, P. J. Brown, J. M. Carpenter, G. Lander, R. Pynn, J. M. Rowe, O. Schärpf, V. F. Sears and B. T. M. Willis. ''International Tables for Crystallography'' (2006). Vol. C, ch. 4.4, pp. 430-487 [http://dx.doi.org/10.1107/97809553602060000594 doi:10.1107/97809553602060000594] | ||

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− | + | [[Category:Physical properties of crystals]] | |

− | + | [[Category:Structure determination]] | |

+ | [[Category:X-rays]] |

## Latest revision as of 18:09, 8 November 2017

Facteur de diffusion atomique (*Fr*). Atomformfaktor, Formfaktor (*Ge*). Fattore di diffusione atomico (*It*). 原子散乱因子 (*Ja*). Factor de forma atómica (*Sp*).

## Definition

A measure of the scattering power of an isolated atom. Also known as the **atomic form factor**. The scattering factor depends on the scattering amplitude of an individual atom, on the Bragg angle and the type of radiation involved.

## X-ray scattering

The scattering from a crystal of an X-ray beam results from the interaction between the electric component of the incident electromagnetic radiation and the electrons in the crystal. Tightly bound electrons scatter coherently (Rayleigh scattering); free electrons scatter incoherently (Compton scattering). The scattering process from atomic electrons in a crystal lattice has both coherent and incoherent components, and is described as Thomson scattering.

The scattering amplitude from a neutral atom depends on the number of electrons (*Z* = the atomic number) and also on the Bragg angle θ – destructive interference among waves scattered from the individual electrons reduces the intensity at other than zero scattering angle. For θ = 0 the scattering amplitude is normally equal to *Z*. However, the scattering factor is modified by anomalous scattering if the incident wavelength is near an absorption edge of the scattering element.

The X-ray scattering factor is evaluated as the Fourier transform of the electron density distribution of an atom or ion, which is calculated from theoretical wavefunctions for free atoms.

## References

*Electron diffraction*: C. Colliex, J. M. Cowley, S. L. Dudarev, M. Fink, J. Gjønnes, R. Hilderbrandt, A. Howie, D. F. Lynch, L. M. Peng, G. Ren, A. W. Ross, V. H. Smith Jr, J. C. H. Spence, J. W. Steeds, J. Wang, M. J. Whelan and B. B. Zvyagin.*International Tables for Crystallography*(2006). Vol. C, ch. 4.3, pp. 259-429 doi:10.1107/97809553602060000593*Intensity of diffracted intensities*: P. J. Brown, A. G. Fox, E. N. Maslen, M. A. O'Keefe and B. T. M. Willis.*International Tables for Crystallography*(2006). Vol. C, ch. 6.1, pp. 554-595 doi:10.1107/97809553602060000600*Neutron techniques*: I. S. Anderson, P. J. Brown, J. M. Carpenter, G. Lander, R. Pynn, J. M. Rowe, O. Schärpf, V. F. Sears and B. T. M. Willis.*International Tables for Crystallography*(2006). Vol. C, ch. 4.4, pp. 430-487 doi:10.1107/97809553602060000594