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

• A. collimation
• B. HVL
• C. attenuation
• D. filtration

Answer: (C)

Attenuation is the reduction in X-ray beam intensity as it passes through matter due to absorption and scattering. When photons interact with material, some are absorbed (removing them from the beam) and some are scattered (deflected out of the primary beam). The remaining photons that emerge form an attenuated beam. The extent of attenuation depends on the material’s density and atomic number and on the photon energy, and it follows I = I0 e^{-μx}, where μ is the linear attenuation coefficient and x is the material thickness.

Collimation shapes the beam but doesn’t describe the material interactions that reduce intensity. Filtration removes low-energy photons from the beam to improve quality and reduce dose, but it’s not the process of attenuation through the material. HVL, or half-value layer, is a measure of beam penetrability (the thickness needed to cut the intensity in half) and relates to attenuation but is a parameter, not the process itself.