The most sizable component of attenuation is which of the following?

• A. Scattering
• B. Reflection
• C. Diffraction
• D. Absorption

Answer: (D)

Attenuation is the reduction of beam intensity as it travels through a material, caused by interactions that remove photons from the forward stream. The main bulk processes are absorption and scattering, while reflection and diffraction are not the dominant contributors inside a bulk medium. Absorption directly removes photons by transferring their energy to the material (often warming it), which reduces the number reaching the detector in the forward direction more effectively than scattering does. Scattering redirects photons, and some of those redirected photons may still reach the detector depending on geometry, so the forward-beam loss from absorption tends to be the largest factor in typical materials and energies used in this context.