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 \(\theta < \text{ca.}\ 5\,°\).
  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 \(R_{\theta}\).
Purple Book, 1st ed., p. 65 [Terms] [Book]