Problem 6.139

What metal has in its absorption spectrum the difference between the frequencies of X-ray $K$ and $L$ absorption edges equal to $\Delta \omega=6.85 \cdot 10^{18} \mathrm{~s}^{-1} ?$

Z=1+\sqrt{4 \Delta \omega / 3 R}=22, \text { titanium. }

Properties of Atoms. Spectra.