Which barrier attenuates stray radiation (scatter)?

• A. Primary Protective Barrier
• B. Secondary Protective Barrier
• C. Lead shield
• D. Exposure barrier

Answer: (B)

Scatter radiation is the radiation that results when the primary x-ray beam interacts with matter and travels in various directions with lower energy. To protect personnel from this stray radiation, shielding is designed in two ways: the primary protective barrier blocks the direct, unaltered primary beam, while the secondary protective barrier intercepts and attenuates radiation that is not the primary beam—namely scatter and leakage. Since scatter comes off the patient and can escape outside the primary beam’s path, the barrier specifically designated to reduce this stray radiation is the secondary protective barrier. Portable lead shields or aprons protect an individual at a local level, but they’re not the architectural barrier that attenuates room-wide scatter.