What is the SI unit of exposure in radiation measurement?

• A. Gray (Gy)
• B. Coulomb per kilogram (C/kg)
• C. Rad
• D. Sievert (Sv)

Answer: (B)

The SI unit of exposure in radiation measurement is the Coulomb per kilogram (C/kg). Exposure specifically refers to the amount of ionization produced by X-rays or gamma rays in air, and it is measured in terms of charge per mass of air. Using C/kg allows for a standardized measurement that relates to the biological effects of radiation exposure.

While other options like Gray (Gy) and Sievert (Sv) are also related to radiation measurement, they are used for different purposes. Gray measures absorbed dose (the energy deposited in matter), and Sievert accounts for biological effects of ionizing radiation, incorporating the quality factor of the radiation type. Rad is an older unit of absorbed dose that has been largely replaced by the Gray in SI units. Hence, the Coulomb per kilogram is the correct choice as it directly quantifies exposure in the context of air ionization.