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Transition energies

The transition energies can be approximately calculated by the use of Moseley's law. For example, E K α = 3 4 (Z − 1) 2 R y ≈ 10.2 (Z − 1) 2 e V {\displaystyle E_{K\alpha }={\frac {3}{4}}(Z-1)^{2}Ry\approx 10.2(Z-1)^{2}~\mathrm {eV} }, where Z is the atomic number and Ry is the Rydberg energy. The energy of the iron (Z = 26) K-alpha, calculated in this fashion, is 6.375 keV, accurate within 1%. However, for higher Z' s the error grows quickly.