# 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