Index

Image dictionary (imgCIF) version 1.3.2

_diffrn_radiation.polarizn_source_ratio

Definition:

   (Ip-In)/(Ip+In), where Ip is the intensity
   (amplitude squared) of the electric vector in the plane of
   polarization and In is the intensity (amplitude squared)
   of the electric vector in the plane of the normal to the
   plane of polarization.

   In the case of an unpolarized beam, or a beam with true
   circular polarization, in which no single plane of
   polarization can be determined, the plane is to be taken
   as the XZ plane and the normal is parallel to the Y axis.

   Thus, if there was complete polarization in the plane of
   polarization, the value of 
   _diffrn_radiation.polarizn_source_ratio would be 1, and 
   for an unpolarized beam 
   _diffrn_radiation.polarizn_source_ratio would have a 
   value of 0.

   If the X axis has been chosen to lie in the plane of
   polarization, this definition will agree with the definition
   of 'MONOCHROMATOR' in the Denzo glossary, and values of near
   1 should be expected for a bending-magnet source.  However,
   if the X axis were perpendicular to the polarization plane 
   (not a common choice), then the Denzo value would be the 
   negative of _diffrn_radiation.polarizn_source_ratio.

   See http://www.hkl-xray.com for information on Denzo and
   Otwinowski & Minor (1997).

   This differs both in the choice of ratio and choice of
   orientation from _diffrn_radiation.polarisn_ratio, which,
   unlike _diffrn_radiation.polarizn_source_ratio, is
   unbounded.
   
   Reference: Otwinowski, Z. & Minor, W. (1997). 'Processing of 
   X-ray diffraction data collected in oscillation mode.' Methods 
   Enzymol. 276, 307-326.

Type: float

Mandatory item: no

Category: diffrn_radiation