In physics, the atomic form factor, or atomic scattering factor, is a measure of the scattering amplitude of a wave by an isolated atom. The atomic form factor depends on the type of scattering, which in turn depends on the nature of the incident radiation, typically X-ray, electron or neutron. The common feature of all form factors is that they involve a Fourier transform of a spatial density distribution of the scattering object from real space to momentum space (also known as reciprocal space). For an object that is spherically symmetric, the spatial density distribution can be expressed as a function of radius, so that the form factor, is defined as :
,
where is the spatial density of the scatterer about the center of mass of the scatterer, and is the momentum transfer. As a result of the nature of the Fourier transform, the broader the distribution of the scatterer in real space, the narrower the distribution of in ; i.e., the faster the decay of the form factor.
For crystals, atomic form factors are used to calculate the structure factor for a given Bragg peak of a crystal.
Read more about Atomic Form Factor: X-ray Form Factor, Electron Form Factor, Neutron Form Factor
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