view article

Figure 3
The primary slits are closed down to the size of the crystal, while the secondary slits are opened slightly larger. This shields the detector from the X-ray scatter of the primary slits and avoids the secondary slits contributing more X-ray scatter. A third series of guard slits, which are opened wider than the previous two, are inserted just prior to the crystal to further screen out the X-ray scatter from the slits and air upstream of the crystal. When the slits are correctly aligned, the largest contribution to low-angle X-ray scatter will come from the transmitted X-ray beam traveling through air. If the crystal-to-detector distance must be large, then a He cone should be set up to minimize the scattering from air. Some scattering will arise from the entrance window of the He cone and ideally the entire assembly (crystal, cryostat, slits etc.) should be encased in a He atmosphere and a He cryostat should be used.

Journal logoBIOLOGICAL
ISSN: 1399-0047
Follow Acta Cryst. D
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds