What factor governs attenuation of a radiation beam's intensity as it passes through an absorber?

The attenuation of a radiation beam's intensity as it passes through an absorber is primarily governed by the specific medium's density. As radiation passes through a material, different densities absorb and scatter photons to varying extents. A denser medium usually contains more atoms per unit volume, offering a higher probability for interactions with incoming radiation, which results in greater attenuation.

This phenomenon is evident when considering materials used in radiation shielding. For example, lead is denser than aluminum and provides superior attenuation of x-rays or gamma rays due to its high atomic number and density, leading to more effective absorption of radiation.

While the energy of the radiation does influence how much attenuation occurs, it primarily affects the type of interactions (e.g., photoelectric effect vs. Compton scattering) that take place within the absorber, making it a secondary consideration compared to the direct impact of the absorber’s density.

The thickness of the absorber traversed does contribute to the overall attenuation—greater thickness typically results in more attenuation—but it is the density of the material that is the fundamental factor determining how effectively the material can attenuate radiation.

Time is generally not a factor in attenuation, as it does not directly relate to how radiation interacts with materials. Therefore, the specific medium's density is the most