Which of the following is NOT a primary control method for radiation exposure?

• A. Ventilation
• B. Time
• C. Distance
• D. Shielding

Answer: (A)

The main idea is that reducing radiation exposure relies on three direct controls: time, distance, and shielding. Limiting the time near the source lowers the dose; increasing the distance from the source reduces exposure due to the inverse-square relationship; and shielding provides a physical barrier to attenuate or block the radiation. Ventilation, while useful for air quality and reducing inhalation of airborne contaminants (internal exposure), does not directly reduce the external radiation dose from a source. Therefore it is not considered a primary control method for radiation exposure.