**Definition:**

Beam crossfire correlation in degrees squared 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 collimation. 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 for some synchrotrons, this value is specified in milliradians squared, in which case a conversion is needed. To convert a value in milliradians squared to a value in degrees squared, multiply by 0.180**2 and divide by pi**2.

**Type:** float

**Mandatory item:** no

Enumeration default: 0.0

**Category:** diffrn_radiation

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