(IUCr) CIF Definition save__diffrn_radiation.polarizn_source_ratio

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Index

##### Image dictionary (imgCIF) version 1.5.4

# _diffrn_radiation.polarizn_source_ratio

Name:
`'_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

The permitted range is [-1.0, 1.0]

Category: diffrn_radiation

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