Rayleigh ratio

The quantity used to characterize the scattered intensity at the scattering angleθ, defined as R θ = i θ r 2 I f V, where I is the intensity of the incident radiation, i θ is the total intensity of scattered radiation observed at an angleθ 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 = cos 2 ⁡ θ for horizontally polarized light and f = 1 + cos 2 ⁡ θ 2 for unpolarized light.
  2. For small-angleneutronscattering, f = 1.
  3. For small-angle X-ray scattering, f ≈ 1, if θ < ca. 5 °.
  1. The dimension of R θ is length −1.
  2. In small-angleneutronscattering the term cross-section is often used instead of R θ; the two quantities are identical.
  3. An alternative recommended symbol is R θ.
Purple Book, p. 65