What does the x-ray unit of exposure define?

The x-ray unit of exposure is defined as Röentgen. The Röentgen is a traditional unit that was used specifically to measure the amount of ionization produced in air by x-ray and gamma radiation. It provides a direct measure of the exposure to ionizing radiation and is specifically applicable to x-rays and gamma rays. This unit is related to the amount of energy these forms of radiation deposit in air, which is crucial for understanding their potential biological effects and for regulatory purposes within the field of radiation protection.

Air kerma, expressed in units like Gray, describes the kinetic energy released in air per unit mass, and is more focused on the energy transfer aspect rather than the exposure itself. Gray is a unit of absorbed dose, measuring the amount of radiation energy absorbed by matter, while Sievert is a unit of dose equivalent, which takes into account the biological effects of different types of radiation. Each of these units serves specific purposes within the context of radiation measurement, but when specifically addressing the unit of exposure from an x-ray perspective, Röentgen is the appropriate choice.