Which of the following describes external radiation exposure reduction methods?

• A. Shielding with dense materials
• B. Waiting for short-lived isotopes to decay
• C. Cleaning surfaces (decontamination)
• D. All of the above

Answer: (D)

External exposure can be reduced by lowering the radiation that reaches a person through different approaches. Shielding with dense materials blocks or attenuates the radiation, so the dose rate at the person’s location drops. Waiting for short-lived isotopes to decay lowers the amount of radioactivity present over time, which reduces the ongoing external exposure. Cleaning surfaces (decontamination) removes radioactive contaminants from objects and areas, shrinking the radiation field around them. Since each of these methods contributes to reducing external dose, combining them covers all the common ways to protect people, so all of the above describes external radiation exposure reduction.