What is the process called when radiation loses intensity as it passes through matter?

• A. Attenuation
• B. Radioactive contamination
• C. Biologic half-life
• D. MRI

Answer: (A)

Attenuation is the process by which radiation loses intensity as it travels through matter. This happens because the material absorbs part of the energy and also scatters some of the radiation, removing energy from the beam. The amount of attenuation depends on the radiation’s energy, the material’s density and composition, and the thickness of the material; denser or thicker materials cause more attenuation, and higher-energy radiation tends to penetrate more with less attenuation. Often this loss of intensity is described by an exponential decrease as the radiation passes through the material. The other options refer to different concepts: radioactive contamination is unwanted radioactive material on surfaces or people; biologic half-life is the time needed for the body to reduce radioactive material; MRI is an imaging technique that uses magnetic fields, not attenuation of radiation. So attenuation is the correct term.