What is the energy released when a K-shell vacancy in tungsten is filled by an L-shell electron?

• A. 57.5 keV
• B. 66.5 keV
• C. 72.5 keV
• D. 69.0 keV

Answer: (A)

When a vacancy in the K-shell is filled by an electron from the L-shell, energy is released as a characteristic X-ray photon. The energy of that photon equals the difference between the binding energy of the K-shell and the binding energy of the L-shell involved in the transition. For tungsten, the K-shell binding energy is about 69.5 keV and the L-shell binding energy is around 12 keV, so the emitted photon has roughly 57.5 keV of energy. That value represents the K–L transition energy (the K-alpha line) and is the appropriate energy released in this process. The other numbers would correspond to different shell differences or exceed the available energy for this transition, so they don't match the K–L emission in tungsten.