Re-thinking the role of the beamstop at a synchrotron-based protein crystallography beamline

A 1 mm vertical-profile X-ray beamstop has been designed to operate in the energy range 6-20 keV. The relationship between the beamstop-to-sample distance and air scatter is discussed with the intent of establishing criteria for optimal beamstop positioning during an experiment. Different choices for beamstop materials are described with respect to stopping power, fluorescence and scattering from the surface. Suggestions for improvements in beamstop design are presented which are applicable for future automation and equipment safety. All work was performed on the Structural Biology Center insertion-device beamline, 19ID, at the Advanced Photon Source.