Reduction of parasitic scattering in small-angle X-ray scattering by a three-pinhole collimating system

A series of experiments have been undertaken on the Oak Ridge National Laboratory (ORNL) 10 m small-angle X-ray scattering (SAXS) camera to provide quantitative data on the level of background (parasitic) scattering generated by different types of bevelled collimating slits. The addition of a third (guard) slit, positioned close to the sample, resulted in a reduction of over an order of magnitude in the parasitic background generated by the best two-slit combination of collimating slits. This made it possible to reduce the size of the beamstop, permitting useful data to be collected down to a value of the scattering vector Q = 4πλ⁻¹sinθ ≃ 3 × 10⁻³ Å−¹, where λ is the wavelength, and 2θ is the angle of scatter. This permits the resolution of distances d ~ 2π/Q up to 2000 Å.