Final answer:
The primary barriers in a radiographic room, such as lead walls, consist of lead shielding that is thick enough to effectively block gamma emissions.
Step-by-step explanation:
The primary barriers in a radiographic room, such as lead walls, are made of high-density materials to effectively shield against gamma emissions. Gamma rays are usually blocked effectively by lead shielding. The thickness of the shielding is crucial in determining the effectiveness of the protection offered by the lead.