Which statement describes the Distance concept in radiation protection?

Which statement describes the Distance concept in radiation protection?

• A. Time should be minimized
• B. Shielding should be worn
• C. Distance between source and exposed should be as great as possible
• D. Exposure should be avoided by shielding only

Answer: (C)

Distance from the radiation source controls exposure because radiation intensity follows the inverse square law: as you increase distance, dose falls off rapidly. Doubling distance reduces exposure to one-quarter, and tripling distance reduces it to one-ninth. This makes maximizing the distance between the source and the person exposed the most effective way to lower dose, so that statement best describes how the Distance concept works. Shielding and minimizing time address other protective principles—shielding blocks or attenuates radiation, and reducing time lowers dose by shortening exposure duration—so they aren’t describing the distance-based method. In practice, use the greatest feasible distance, and combine with shielding and reduced exposure time as appropriate.

Distance from the radiation source controls exposure because radiation intensity follows the inverse square law: as you increase distance, dose falls off rapidly. Doubling distance reduces exposure to one-quarter, and tripling distance reduces it to one-ninth. This makes maximizing the distance between the source and the person exposed the most effective way to lower dose, so that statement best describes how the Distance concept works. Shielding and minimizing time address other protective principles—shielding blocks or attenuates radiation, and reducing time lowers dose by shortening exposure duration—so they aren’t describing the distance-based method. In practice, use the greatest feasible distance, and combine with shielding and reduced exposure time as appropriate.