The process by which an X-ray beam is reduced in intensity by absorption or scattering as it passes through material is termed:

• A. Collimation
• B. HVL
• C. Attenuation
• D. Filtration

Answer: (C)

Attenuation is the reduction of X-ray beam intensity as it passes through matter, caused by absorption and scattering. As photons meet atoms, some are absorbed (photoelectric interactions) and others are scattered (Compton interactions), removing photons from the original beam or altering their direction. The surviving photons form a weaker beam, described by I = I0 e^{-μx}, where μ depends on the material and photon energy. The other terms refer to different concepts: filtration removes low-energy photons to improve beam quality, collimation shapes the beam geometry, and the half-value layer is a quantitative measure of how much material is needed to cut the beam’s intensity in half.