Air kerma is measured in which unit?

Air kerma is a measure of the energy transferred from ionizing radiation to air, indicative of the radiation dose delivered to that air. The appropriate unit for air kerma is Joule per kilogram (J/kg). This unit expresses the amount of energy (in joules) imparted to a mass of air (in kilograms) as radiation passes through it.

Gray (Gy) is indeed a unit of dose that describes the energy absorbed per unit mass of tissue, but it is specifically used for absorbed dose rather than air kerma. Similarly, Rad is an older unit of absorbed dose, and while it also relates to energy absorbed by matter, it is not the unit used specifically for air kerma. The Sievert (Sv) is used to quantify biological effects of radiation, taking into account the type of radiation and its impact on health, which is different from the physical measurement of air kerma. Therefore, Joule per kilogram correctly represents the magnitude of energy transferred to air, making it the accurate choice in this context.