Which measure describes the ionization produced in air?

• A. Effective dose
• B. Exposure
• C. Absorbed dose
• D. Equivalent dose

Answer: (B)

Ionization produced in air is what exposure measures. When high-energy radiation like X-rays or gamma rays passes through air, it creates ions by knocking electrons off air molecules. Exposure quantifies how much ionization occurs per unit mass of air, historically described by the amount of electric charge produced in a kilogram of air (in old units, the roentgen; in SI terms, coulombs per kilogram). This is different from energy actually deposited in matter—absorbed dose—which focuses on energy transfer per unit mass of a material, not the ionization in air itself. It’s also separate from equivalent dose and effective dose, which translate absorbed energy into potential biological risk using weighting factors for radiation type and tissue. So exposure is the measure that directly describes the ionization produced in air.