For a certain target atom, the K-shell binding energy is 25 keV and the L-shell binding energy is 4 keV. Its Kα photon energy is therefore approximately 21 keV. What is the minimum accelerating potential required in an X-ray tube before this Kα radiation can be produced?
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Question

For a certain target atom, the K-shell binding energy is 25 keV and the L-shell binding energy is 4 keV. Its Kα photon energy is therefore approximately 21 keV. What is the minimum accelerating potential required in an X-ray tube before this Kα radiation can be produced?

Options

G1 Physics · Accepted Answer

The Kα photon energy is the difference between the K- and L-shell binding energies: E(Kα) = 25−4 = 21 keV. However, before this photon can be emitted, a K-shell vacancy must first be created. The incident electron must therefore have at least the full K-shell binding energy of 25 keV. Hence the minimum accelerating voltage is 25 kV. Correct option: C.