  Gain calibration of x-ray area detectors is a challenge due to the inability
to generate an x-ray flat field at the selected photon energy that the beamline
operates at, which has a strong influence on the detector's gain behavior. A
method is presented in which a gain map is calculated without flat field
measurements. Rather, a series of quick scattering measurements from an
amorphous scatterer is used to calculate a gain map. The ability to rapidly
obtain a gain map allows for a recalibration of an x-ray detector as needed
without significant expenditure of either time or effort. Area detectors on the
beamlines used, such as the Pilatus 2M CdTe or Varex XRD 4343CT, were found to
have gains which drift slightly over timescales of several weeks or after
exposure to high photon flux, suggesting the need to more frequently
recalibrate for detector gain.
