Final answer:
Aluminum is typically used as a filter for the primary beam in medical imaging due to its ability to absorb X-ray photons effectively while maintaining image quality. Lead is used to block more penetrating radiation such as gamma rays. the correct option is (a).
Step-by-step explanation:
The material generally used in the construction of a filter for the primary beam in medical imaging and radiation shielding is aluminum. This is because aluminum is effective in filtering out certain energies of X-ray photons by absorbing them, which reduces the intensity of the primary beam without significantly compromising the quality of the diagnostic image.
Other materials have different levels of radiation shielding effectiveness. Lead is known for its high-density and is thus much more effective at blocking gamma emissions. It is often used in radiation protection to shield against more penetrating types of radiation. Materials like paper, metal, concrete, and lead can block different types of radiation with varying effectiveness. The types of radiation, from least to most penetrating, are arranged as alpha < beta < neutron < gamma. Thus, a filter made of aluminum is generally chosen for its balance between protection and image quality in the context of X-ray imaging.