Absorbed dose and dose equivalent units?

• A. rad and rem
• B. gray and sievert
• C. rem and gray
• D. rad and gray

Answer: (B)

The main idea is distinguishing the units used for two related but different radiation quantities: absorbed dose and dose equivalent. Absorbed dose measures how much energy is deposited in tissue per unit mass, so its unit is the gray (Gy), where 1 Gy equals 1 joule per kilogram. Dose equivalent, on the other hand, accounts for the potential biological effect of the radiation, which depends on the type of radiation; its unit is the sievert (Sv), where 1 Sv equals 1 Gy times a radiation weighting factor.

Using the SI system, gray and sievert are the standard pair for these quantities, making them the best answer. The other options mix older units—rad for absorbed dose and rem for dose equivalent—which are not the SI units, even though you can convert between them (1 Gy = 100 rad; 1 Sv = 100 rem). For most modern practice and exams, gray and sievert are the expected units.