What event leads to the emission of a characteristic X-ray?

• A. Neutron capture
• B. Inner-shell electron ejection followed by outer-shell filling emitting X-rays
• C. Nuclear decay without electron transitions
• D. Electron-positron annihilation

Answer: (B)

Characteristic X-ray emission happens when an inner-shell electron is removed from an atom and an electron from a higher shell drops into that vacancy. As the electron moves to a lower energy level, energy is released as a photon. The energy of that photon corresponds to the difference between the two shells and is specific to the element, giving distinct, element-identified X-ray lines. In XRF analysis, the incident radiation or particle knocks out a core electron, creating the vacancy, and the subsequent transition of a higher-shell electron produces these characteristic X-rays. Other processes, like nuclear transitions or electron-positron annihilation, involve different kinds of radiation and do not produce the element-specific characteristic X-ray lines described here.