If the intensity of the x-ray beam increases, how are exposure and air kerma affected?

• A. Exposure increases and air kerma decreases
• B. Exposure decreases and air kerma increases
• C. Exposure decreases and air kerma decreases
• D. Exposure increases and air kerma increases

Answer: (D)

Increasing the x-ray beam intensity means more photons are traveling through the air per unit area. More photons cause more ionizations in the air, so exposure—the amount of ionization produced in air—rises. Air kerma is the energy delivered to the air by those photons per unit mass; with more photons carrying energy, more energy is deposited, so kerma also rises. Since both exposure and air kerma scale with photon fluence, they increase together when beam intensity increases, assuming the beam spectrum and geometry remain the same.