Derived Air Concentration (DAC) represents what?

• A. The dose rate at the skin surface.
• B. The total body burden of radionuclide.
• C. The maximum activity of a source.
• D. The concentration in air that would deliver a specified dose.

Answer: (D)

Derived Air Concentration is the amount of radioactive material per unit volume of air that would deliver a specified dose if that air is inhaled over a defined exposure period (typically a year) at a given breathing rate. In practice, it converts the annual limit on intake into an air concentration by dividing the ALI by the total volume of air a person breathes in during the year. This makes DAC a practical standard for comparing real airborne concentrations to regulatory limits and guiding ventilation and air monitoring decisions. The chosen interpretation matches the concept exactly: it describes the air concentration that would produce the specified dose.