Problem 5.271

A narrow X-ray beam falls on a NaCl single crystal. The least angle of incidence at which the mirror reflection from the system of crystallographic planes is still observed is equal to \(\alpha=\) \(=4.1^{\circ} .\) The interplanar distance is \(d=0.28 \mathrm{nm}\). How high is the voltage applied to the X-ray tube?