Index

Image dictionary (imgCIF) version 1.5.4

_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

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