Problem 6.138

When the voltage applied to an X-ray tube increased from \(V_{1}=10 \mathrm{kV}\) to \(V_{2}=20 \mathrm{kV}\), the wavelength interval between the \(K_{\alpha}\) line and the short-wave cut-off of the continuous X-ray spectrum increases by a factor \(n=3.0 .\) Find the atomic number of the element of which the tube's anticathode is made.