What term describes the reduction of radiation intensity as the primary beam passes through material?

The term that describes the reduction of radiation intensity as the primary beam passes through material is "attenuation." Attenuation refers to the process by which the intensity of radiation decreases due to interactions with the material the radiation travels through. This reduction in radiation can happen through various mechanisms, including absorption and scattering.

In contrast, absorption specifically relates to the process where radiation energy is absorbed by the material, contributing to attenuation but not encompassing all aspects of it. Transmission refers to the passage of radiation through a material without any decrease in intensity, which is the opposite of what attenuation entails. Reflection involves the bouncing back of radiation from a surface, which does not contribute to the reduction of intensity as it passes through a material. Therefore, attenuation provides the most comprehensive description of the overall decrease in radiation intensity when interacting with different materials.