Rayleigh ratio

The Rayleigh ratio is a quantity used to characterize the scattered intensity as a function of scattering angle $q$, and is defined as

:$R(\; heta\; )\; =\; frac\{I\_\; heta\; r^2\}\{I\; f\; V\}$

where $I$ is the intensity of theincident radiation, $I\_\; heta$ is the total intensity of scattered radiation observedat an angle $q$ and a distance $r$ from the point of scattering and $V$ is thescattering volume. The factor $f$ is introduced to compensate for polarization phenomena, and is dependent of the type of radiation used as follows:

1. For light scattering, $f$ depends on the polarization of the incident beam, and is$f=1$ for vertically polarized light, $f=cos^2\; (q)$ for horizontally polarized lightand $f\; =\; 0.5(1\; +\; cos^2\; (q))$ for unpolarized light.

2. For small-angle neutron scattering, $f=1$.

3. For small-angle X-ray scattering, $f>>1$, if q < ca. 5°.

Notes:

1. The dimension of R(q) is an inverse length.

2. In small-angle neutron scattering the term cross-section is frequently usedin place of $R(q)$.

3. IUPAC also recommends the symbol $R\_q$.

References

* http://www.iupac.org/goldbook/R05159.pdf