Item _diffrn_radiation.polarizn_source_ratio
Description
(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 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 be taken
as the X-Z plane, and the normal is parallel to the Y-axis.
Thus, if we had complete polarization in the plane of
polarization, the value of
'_diffrn_radiation.polarizn_source_ratio' would
be 1, and an unpolarized beam 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, for some reason to be, say,
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
Z. Otwinowski and W. Minor, "Processing of X-ray
Diffraction Data Collected in Oscillation Mode", Methods
in Enzymology, Volume 276: Macromolecular Crystallography,
part A, p.307-326, 1997,C.W. Carter, Jr. & R. M. Sweet,
Eds., Academic Press.
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.
Category
diffrn_radiation
Mandatory Code
no
Data Type Code
float
Enumeration Range
| Minimum Value |
Maximum Value |
| 1.0 |
1.0 |
| -1.0 |
1.0 |
| -1.0 |
-1.0 |
