In a CR phosphor layer, which interaction is responsible for absorbing diagnostic x-ray photons?

• A. Classical
• B. Compton
• C. Photoelectric
• D. Characteristic

Answer: (C)

In a CR phosphor layer, absorbing diagnostic x-ray photons mainly occurs through the photoelectric effect. This interaction is highly probable in high‑Z phosphor materials at the lower end of diagnostic energies, where the photon is absorbed and an inner-shell electron is ejected. The vacancy is then filled, and that energy drives the luminescent centers to emit visible light, which is what the reader detects.

Compton scattering transfers only part of the photon’s energy to an outer electron and leaves the photon scattered; it does not fully absorb the photon, so it’s less effective at producing the light signal in the phosphor. The term related to characteristic x-rays describes photons emitted by the material after inner-shell ionization, not the absorption process itself.