Parallel-beam geometry for single-crystal diffraction

Reflection from a perfect crystal is used to produce a parallel beam of Kα₁ radiation. The losses due to large distances, which are needed for elimination of the Kα₂ component, are compensated by a totally reflecting guide tube. The measured flux of Kα₁ from a Cu-target X-ray tube at 40 kV and 40 mA was 5 × 10⁵ counts s⁻¹ on an area of 0.5 mm², when an Si(220) monochromator and a glass guide tube were used. It is estimated that 1 × 10⁷ counts s⁻¹ are available with a Ge(111) monochromator and a gold-plated guide tube. The angular resolution is about 0.1 mrad.