The reason is that wavelength resolution is unable to separate CrKα2 from CrKα1. Often, we need more than one type of crystal to obtain the whole range of wavelength dispersion from a specimen, because the limitation of wavelength rages by the crystal’s d-spacing. For example, Figure 6.8 show the spectra of nickel-based alloy obtained by LiF and TAP analyzing crystals. The spectrum obtained with LiF covers a short wavelength and that obtain with TAP covers along wavelength range.