X-Ray to Visible Wavelength Ratios

The lattice repeat distance of a nearly perfect single crystal of silicon has been measured in terms of the visible wavelength of a stabilized He-Ne laser. This crystal subsequently has been used to diffract reference x-ray lines (Cu Kα₁, Mo Kα₁) thereby establishing their wavelength relative to visible standards. In terms of the x-ray scale in which λ(CuKα₁)=1.537400 kxu, the conversion factor is ΛCu=1.0020802 {}/kxu (1 ppm); if λ(MoKα₁)=0.707831 kxu, ΛMo=1.0021017 {}/kxu (0.6 ppm).