Which unit is used to express the equivalent dose?

• A. Gray (Gy)
• B. Sievert (Sv)
• C. Coulombs per kilogram (c/kg)
• D. Becquerel (Bq)

Answer: (B)

Equivalent dose reflects not just how much energy is deposited in tissue, but how biologically harmful that energy could be, and it does so by incorporating a radiation-weighting factor. The unit Sievert is used because it combines the absorbed dose with this factor, giving a measure of potential biological effect. For X-rays, the weighting factor is 1, so the equivalent dose in Sieverts equals the absorbed dose in Grays (1 Gy = 1 Sv). Gray measures energy deposited per kilogram, but it doesn’t account for how different radiations affect living tissue. Coulombs per kilogram is exposure in air, and Becquerel is a measure of radioactive decay rate, not dose. Thus, Sievert is the appropriate unit for expressing equivalent dose.