Define Derived Air Concentration (DAC) and explain its use in radiation protection decision-making.

• A. DAC is the maximum contamination limit in soil.
• B. A DAC is the dose rate limit established for a given area.
• C. A DAC is the concentration of radioactive material in air that would deliver a specified limit dose in a given time.
• D. DAC measures the activity per unit volume.

Answer: (C)

Derived Air Concentration is the concentration of radioactive material in air that would deliver a specified dose to a person who breathes that air for a defined period. It ties dose limits to an airborne concentration so you can judge whether an operation is within protection goals. In practice, you select a dose limit (for workers, an annual limit is typical) and use the radionuclide’s inhalation dose coefficient and a realistic breathing rate and exposure time to compute the corresponding DAC. This makes the DAC a practical threshold: if the actual airborne concentration is below the DAC, the protection targets are met; if it’s above, you implement controls such as ventilation, containment, or respiratory protection. DACs are radionuclide- and scenario-specific, reflecting how different materials and exposure times affect dose.

This isn’t a soil contamination limit, nor a dose-rate limit for a location, nor merely a measure of activity per unit volume. It’s a derived, protective concentration in air used to make decisions about how to control airborne radioactivity.