## Rayleigh ratio

https://doi.org/10.1351/goldbook.R05159
The quantity used to characterize the scattered intensity at the @S05488@ $$\theta$$, defined as $$R(\theta) = \frac{i_{\theta }\,r^{2}}{I\,f\,V}$$, where $$I$$ is the intensity of the incident radiation, $$i_{\theta}$$ is the total intensity of scattered radiation observed at an @A00346@ $$\theta$$ and a distance $$r$$ from the point of @S05487@ and $$V$$ is the @S05487@ volume. The factor $$f$$ takes account of @P04712@ phenomena. It depends on the type of radiation employed.
1. For @L03525@, dependent on the @P04712@ of the incident beam, $$f=1$$ for vertically polarized light, $$f = 1 - \cos^{2}\theta$$ for horizontally polarized light and $$f = 1 + \frac{\cos^{2}\theta}{2}$$ for unpolarized light.
2. For small-@A00346@ @N04116@ @S05487@, $$f=1$$.
3. For small-@A00346@ X-ray @S05487@, $$f \approx 1$$, if $$\theta < \text{ca.}\ 5\,°$$.
Notes:
1. The dimension of $$R(\theta)$$ is $$(\text{length})^{-1}$$.
2. In small-@A00346@ @N04116@ @S05487@ the term cross-section is often used instead of $$R(\theta)$$; the two quantities are identical.
3. An alternative recommended symbol is $$R_{\theta}$$.
Source:
Purple Book, 1st ed., p. 65 [Terms] [Book]