What is the unit of measurement for radiation exposure?

The correct unit of measurement for radiation exposure is Coulombs per kilogram (C/kg). This unit quantifies the amount of ionization produced by radiation in a specified mass of air and is used primarily to gauge the exposure to ionizing radiation.

Coulombs per kilogram reflects the charge of ion pairs generated in air by gamma or X-ray radiation. It provides a direct measurement of how much radiation is delivering energy to the air and potentially could harm humans or other materials.

The other units are related but pertain to different aspects of radiation measurement. Sieverts measures biological effect and is used to account for the biological impact of radiation on human beings, taking into consideration the type of radiation and its energy. Gray quantifies the absorbed dose of radiation, representing the amount of energy deposited in a material, typically tissue, but does not address the ionization per unit mass directly. Rem is also a unit that relates to biological effects similar to the Sievert but is an older term, with one Rem approximately equivalent to 0.01 Sieverts.