Atomic scattering factors
The atomic scattering factors are measures of the scattering power of individual atoms. Each element has a different atomic scattering factor, which represents how strongly x-rays interact with those atoms.
The scattering factor has two components: f_{1} and f_{2}, which describe the dispersive and absorptive components. In other words, f_{2} describes how strongly the material absorbs the radiation, while f_{1} describes the non-absorptive interaction (which leads to refraction).
Contents
Elemental dependence
Because x-ray interactions occur with an atom's electron cloud, the scattering factors increase with number of electrons, and thus with atomic number (Z). However, the relationship between f and Z is not monotonic, owing to resonant (absorption) edges.
Energy dependence
The atomic scattering factors vary with x-ray wavelength. In particular, a given element will have resonant edges at certain energies, where the absorption increases markedly. The dispersive component f_{1} will also vary rapidly in the vicinity of an absorption edge (c.f. Kramers-Kronig relations). In general, absorption decreases with increasing energy (i.e. high-energy x-rays can penetrate more efficiently through materials).
Examples
silicon
gold
Elemental/Energy dependence
Related forms
There are a variety of quantities related to the material's x-ray interaction strength:
- Dispersive atomic scattering factor , the intrinsic interaction of the material.
- Critical angle , the angle below which the beam undergoes total external reflection.
- Critical wave-vector , the momentum transfer (in reciprocal-space) corresponding to the critical angle.
- Real refractive index , the refractive component of the refractive index.
- Real Scattering Length Density , the primary (non-absorptive) component of the scattering contrast.
- Electron Density , the number of electrons per unit volume.
See also absorption length for a comparison of the quantities related to f_{2}.
See Also
- Atomic Form Factor
- Periodic table of atomic scattering factors: Useful tool for looking up the values for any element.
- APS Python code for calculating f
- Online Dictionary of Crystallography: Atomic scattering factor