What unit is used to measure exposure to ionizing radiation?

The correct unit used to measure exposure to ionizing radiation is the Roentgen (R). This unit specifically quantifies the exposure of air to X-rays and gamma radiation based on the amount of ionization produced in air. The Roentgen is historically significant in radiation measurement and is primarily concerned with the direct ionization of radiation in air.

Other units, while related to radiation, serve different purposes. The Sievert (Sv) is a unit that measures the biological effect of radiation, accounting for the type of radiation and its impact on human tissues. The Gray (Gy), on the other hand, measures the absorbed dose of radiation in any material, including biological tissue, indicating the energy deposited per kilogram of mass. The Curie (Ci) is a unit of radioactivity that expresses the amount of radioactive decay occurring in a sample, rather than a direct measure of exposure. Each of these units is relevant in the field of radiation safety and measurement, but the Roentgen is specifically focused on the exposure aspect in air.