Rayleigh ratio 

https://doi.org/10.1351/goldbook.R05159
The quantity used to characterize the scattered intensity at the scattering angle θ, defined as R(θ)=iθr2IfV, where I is the intensity of the incident radiation, iθ is the total intensity of scattered radiation observed at an angle θ and a distance r from the point of scattering and V is the scattering volume. The factor f takes account of polarization phenomena. It depends on the type of radiation employed.
  1. For light scattering, dependent on the polarization of the incident beam, f=1 for vertically polarized light, f=1−cos2⁡θ for horizontally polarized light and f=1+cos2⁡θ2 for unpolarized light.
  2. For small-angle neutron scattering, f=1.
  3. For small-angle X-ray scattering, f≈1, if θ<ca. 5°.
Notes:
  1. The dimension of R(θ) is (length)−1.
  2. In small-angle neutron scattering the term cross-section is often used instead of R(θ); the two quantities are identical.
  3. An alternative recommended symbol is Rθ.
Source:
Purple Book, 1st ed., p. 65 [Terms] [Book]
Citation: 'Rayleigh ratio' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.R05159 RIS BibTex EndNote
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Last revised: February 24, 2014