Cu K-alpha

Copper K-α is an x-ray energy frequently used on labscale x-ray instruments. The energy is 8.04 keV, which corresponds to an x-ray wavelength of 1.5406 Å.

This causes the prefactor in the scattering equation to be:

$k={\frac {4\pi }{\lambda }}=4.0784\,\mathrm {\AA} ^{-1}$