Calculate the ratio of the wavelength of the K_\alpha line for niobium (Nb) to that for gallium (Ga).Take needed data from the periodic table of Appendix G.
THINK The frequency of an x-ray emission is proportional to (Z – 1)², where Z is the atomic number of the target atom.
EXPRESS The ratio of the wavelength λ_{Nb} for the K_\alpha line of niobium to the wavelength λ_{Ga} for the K_\alpha line of gallium is given by
\lambda_{ Nb } / \lambda_{ Ga }=\left(Z_{ Ga }-1\right)^2 /\left(Z_{ Nb}-1\right)^2
where Z_{Nb} is the atomic number of niobium (41) and Z_{Ga} is the atomic number of gallium (31). Thus, \lambda_{ Nb } / \lambda_{ Ga }=(30)^2 /(40)^2=9 / 16 \approx 0.563 .
LEARN The frequency of the K_\alpha line is given by Eq. 40-26:
f=\left(2.46 \times 10^{15} Hz \right)(Z-1)^2 .
\begin{aligned} f & =\frac{\Delta E}{h}=\frac{(10.2 eV )(Z-1)^2}{\left(4.14 \times 10^{-15} eV \cdot s \right)} \\ & =\left(2.46 \times 10^{15} Hz \right)(Z-1)^2 . \end{aligned} (40-26)