In the production of characteristic radiation at a tungsten target, the incident electron:

• A. Ejects inner-shell tungsten electron
• B. Ejects outer-shell electron
• C. Ejects proton
• D. Ejects neutron

Answer: (A)

Characteristic radiation arises when a vacancy is created in an atom’s inner electron shell. The incident electron must have enough energy to ionize that inner shell, ejecting a tungsten inner-shell (K-shell) electron. Once the vacancy exists, an electron from a higher shell drops into the lower level, and the energy released as a photon has a specific, characteristic value for tungsten. That’s why the process hinges on removing an inner-shell electron—the resulting photon energies are unique to the element.

Ejecting an outer-shell electron can occur, but it doesn’t produce the definite inner-shell transition photons that define characteristic radiation. Ejecting a proton or neutron involves nuclear interactions, not the electronic transitions responsible for characteristic X-rays.