Beam crossfire correlation degrees2 between the
crossfire laboratory X-axis component and the crossfire
laboratory Y-axis component (see AXIS category).
This is a characteristic of the X-ray beam as it illuminates
the sample (or specimen) after all monochromation and
This is the mean of the products of the deviations of the
direction of each photon in XZ plane times the deviations
of the direction of the same photon in the YZ plane
around the mean source beam direction. This will be zero
for uncorrelated crossfire.
Note that some synchrotrons, this value is specified in
milliradians2, in which case a conversion would be needed.
To go from a value in milliradians2 to a value in
degrees2, multiply by 0.1802 and divide by \p2.