Which single measure primarily reduces exposure by increasing separation from the source?

• A. Time
• B. Distance
• C. Shielding
• D. Protective clothing

Answer: (B)

Exposure from a radiation source drops dramatically as you increase distance because of the inverse square law: the dose rate falls off with the square of the distance. This makes distance the most effective single way to reduce exposure when you can move away from the source. For example, doubling the distance cuts the dose rate to one quarter, and tripling it reduces it to about one ninth.

Time, shielding, and protective clothing all help, but they don’t increase separation. Time reduces how long you’re exposed, shielding attenuates or blocks some of the radiation, and protective clothing limits contamination and skin dose. None of these directly boost separation from the source as effectively as simply stepping back.