What unit is used to express radiation doses such as equivalent dose and effective dose?

• A. Gray
• B. Sievert
• C. Rontgen
• D. Joule per kilogram

Answer: (B)

Expressing radiation doses in terms of potential biological harm uses the sievert. Absorbed dose measures energy deposited per unit mass and is expressed in gray, which tells you how much energy is delivered but not how harmful it is for living tissue. The equivalent dose refines this by multiplying the absorbed dose by a radiation weighting factor that reflects how different types of radiation affect biological tissue (for X-rays and gamma rays this factor is 1, higher for radiation like alpha particles). The result is expressed in sieverts and represents the biological impact of the radiation type. The effective dose goes further by multiplying the equivalent dose by tissue weighting factors that account for the varying sensitivities of different tissues, giving a single value that estimates overall risk to the person, also in sieverts. So, sievert is the appropriate unit for these dose concepts because it integrates both the type of radiation and the tissue response, whereas gray is just the energy deposited, and older units like the Rontgen describe exposure in air, not the biological effect; joule per kilogram is the physical unit underlying gray but does not directly convey biological risk.