What are the common units used for exposure, absorbed dose, and effective dose?

• A. Exposure: roentgen (R) or coulombs per kilogram in SI; absorbed dose: rad or gray (Gy); effective dose: rem or sievert (Sv).
• B. Exposure: gray (Gy); absorbed dose: roentgen (R); effective dose: sievert (Sv).
• C. Exposure: sievert (Sv); absorbed dose: rem; effective dose: gray (Gy).
• D. Exposure: coulombs per kilogram; absorbed dose: rem; effective dose: roentgen.

Answer: (A)

Understanding the units comes from recognizing three related but different ideas: exposure, absorbed dose, and effective dose. Exposure measures how much ionization is produced in air by radiation and is expressed in roentgens; in SI this is expressed as coulombs per kilogram. Absorbed dose is about how much energy is deposited in a material per unit mass, so the traditional unit is the rad and the SI equivalent is gray (Gy). Effective dose combines dose with tissue‑specific weighting to estimate potential harm, so it uses the rem historically and the SI equivalent is sievert (Sv). Therefore, the standard pairing is exposure in roentgens or C/kg, absorbed dose in rads or Gy, and effective dose in rem or Sv. The other options mix these quantities with the wrong units (for example, using Gray for exposure or roentgen for absorbed dose, which isn’t correct), and ignore that rem and Sv are the units used for the protective, biologically weighted dose.