Which quantity measures energy transferred from photons to air at a point?

Which quantity measures energy transferred from photons to air at a point?

• A. Air kerma (AK)
• B. Effective dose (EfD)
• C. Kerma-area product (KAP)
• D. Absorbed dose

Answer: (A)

Air kerma measures the energy transferred from photons to charged particles in air per unit mass at a point. Kerma (kinetic energy released in matter) specifically quantifies that initial transfer of energy from the photon field to electrons in the medium, and when we talk about air, we call it air kerma. It’s expressed in gray (J/kg) and is used to calibrate radiation exposure at a precise location, before subsequent scattering or energy deposition changes the distribution. Absorbed dose, by contrast, describes the energy actually deposited in a mass after all interactions, which can differ from kerma when energy carriers escape or redistribute. The other options relate to different concepts: effective dose reflects overall stochastic risk across tissues, and kerma-area product combines kerma with beam area to gauge total potential energy delivered to a patient.

Air kerma measures the energy transferred from photons to charged particles in air per unit mass at a point. Kerma (kinetic energy released in matter) specifically quantifies that initial transfer of energy from the photon field to electrons in the medium, and when we talk about air, we call it air kerma. It’s expressed in gray (J/kg) and is used to calibrate radiation exposure at a precise location, before subsequent scattering or energy deposition changes the distribution. Absorbed dose, by contrast, describes the energy actually deposited in a mass after all interactions, which can differ from kerma when energy carriers escape or redistribute. The other options relate to different concepts: effective dose reflects overall stochastic risk across tissues, and kerma-area product combines kerma with beam area to gauge total potential energy delivered to a patient.