| DRAFT DICTIONARY CBF/imgCIF Extensions Dictionary | Draft version 1.5 for comment | 
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Definition:
        The angle in degrees, as viewed from the specimen, between
               the normal to the polarization plane and the laboratory Y
               axis as defined in the AXIS category.
               Note that this is the angle of polarization of the source
               photons, either directly from a synchrotron beamline or
               from a monochromater.
               This differs from the value of
               _diffrn_radiation.polarisn_norm
               in that _diffrn_radiation.polarisn_norm refers to
               polarization relative to the diffraction plane rather than
               to the laboratory axis system.
               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 should be taken
               as the XZ plane and the angle as 0.
               See _diffrn_radiation.polarizn_source_ratio.
Type: float
Mandatory item: no
Category: diffrn_radiation
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