What SI unit is used for absorbed dose?

The SI unit used for absorbed dose is the Gray. This unit quantifies the amount of ionizing radiation energy absorbed by a substance, specifically per kilogram of that substance. One Gray is defined as the absorption of one joule of radiation energy by one kilogram of matter. This measurement is critical in radiation protection and medical physics, as it helps assess the potential biological effects of radiation on human tissue and other materials.

Other units mentioned, while related to radiation, measure different concepts. REM, for example, is a non-SI unit used to express effective dose, combining the absorbed dose with a quality factor to account for the biological impact of different types of radiation. Coulomb/Kilogram is a unit of ionization and not a measure of absorbed dose, as it quantifies the amount of charge per unit mass. Finally, the Becquerel is a unit for radioactivity, representing the activity of a quantity of radioactive material in which one disintegration occurs per second. These distinctions highlight why Gray is the correct answer for absorbed dose.