Which process initiates the emission of characteristic x-rays in XRF?

• A. Exposing the sample to infrared radiation
• B. Bombarding the sample with electrons (not X-rays)
• C. Bombarding the sample with x-rays
• D. Heating the sample to high temperature

Answer: (C)

In XRF, characteristic X-rays appear when the sample is excited by high-energy photons from the primary X-ray source. Those photons have enough energy to eject an inner-shell electron, creating a vacancy. As electrons from higher shells fill that vacancy, energy is released as photons with energies specific to the element—the characteristic X-rays. This X-ray excitation is the standard trigger for the emission used in XRF, which is why bombarding the sample with X-rays is the correct description. Infrared exposure or heating won’t cause inner-shell ionization to produce characteristic X-rays, and while electron bombardment can generate X-rays in other techniques, it’s not the typical excitation method for XRF.