American Registry of Radiologic Technologists (ARRT) Practice Exam

The unit of exposure in air is Roentgen, which quantifies the ionization produced in air by X-rays or gamma rays. Specifically, one Roentgen is defined as the amount of radiation that produces an electric charge of 1 coulomb in 1 kilogram of dry air under standard temperature and pressure conditions. This measurement focuses on the radiation's interaction with air, particularly its ability to ionize atoms, making it essential for understanding radiation doses in environmental and clinical settings. The other units listed, such as Gray (Gy) and Sievert (Sv), relate to absorbed dose and equivalent dose, respectively, and are not specifically designed to measure exposure in air. Gray measures the amount of energy absorbed per unit mass of tissue, while Sievert accounts for the biological effects of different types of radiation. Rad, which is an older unit of absorbed dose, is not commonly used in modern practice and has been largely replaced by Gray. Thus, the choice of Roentgen is correct, as it is specifically tailored to describe exposure in air.