In radiographic imaging phosphor layer, which interaction is primarily responsible for absorbing diagnostic x-ray photons?

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

Answer: (A)

The main idea is that, in phosphor layers used to convert x-rays to light, the dominant way a diagnostic photon is absorbed is through the photoelectric effect. In this process, the incoming photon transfers its energy to an inner-shell electron, ejecting it from the atom. This absorption deposits energy locally in the phosphor, and the resulting excited state leads to luminescence as the atom relaxes, producing the visible light that the detector captures. Compton scattering can occur and also deposits some energy, but it involves the photon being scattered with reduced energy rather than fully absorbed, so it’s not the primary absorption mechanism in this context. The term associated with emitting material after such absorption is characteristic radiation, which describes photons emitted during de-excitation, not the initial absorption process itself. Therefore, photoelectric absorption is the best answer.