The preferred term for radiation exposure is which of the following?

• A. Coulombs per kilogram
• B. Gray
• C. Sievert
• D. Air kerma

Answer: (C)

Exposure in radiology is described today by the quantity air kerma, which stands for kinetic energy released per unit mass of air. It captures the energy transferred from the incident radiation to the air and serves as the input measure for estimating patient skin dose. The unit for air kerma is the gray (Gy), since it expresses energy per mass (joules per kilogram).

Coulombs per kilogram is the older unit historically used for exposure, not the preferred term. The gray represents absorbed dose, the amount of energy deposited in a material, while the sievert accounts for biological effect (equivalent or effective dose). So air kerma is the term that best fits the concept of radiation exposure in this context.