Which statement correctly defines dose equivalent?

• A. Dose equivalent equals absorbed dose times tissue weighting factor
• B. Dose equivalent equals absorbed dose times radiation weighting factor
• C. Dose equivalent equals absorbed dose divided by radiation weighting factor
• D. Dose equivalent equals energy deposited in tissue

Answer: (B)

The key idea is that the biological impact of radiation depends not only on how much energy is deposited, but also on the type of radiation causing that deposition. Dose equivalent combines these factors by multiplying the absorbed dose by a radiation weighting factor that represents how biologically damaging the radiation is.

absorbed dose is the energy deposited per unit mass in tissue, measured in grays. The radiation weighting factor, wR, is dimensionless and reflects the relative biological effectiveness of different radiation types (for example, alpha particles are much more damaging per unit energy than photons). Multiplying these gives the dose equivalent, H = Dabs × wR, with units of sieverts. This allows apples-to-apples comparison of risk across radiation types.

For instance, the same absorbed dose from gamma rays (wR about 1) yields a dose equivalent roughly equal to the absorbed dose, but alpha particles (with a much higher wR) produce a much larger dose equivalent for the same energy deposited, highlighting greater potential biological harm.

The other ideas don’t fit because tissue weighting factors are used to compute effective dose across tissues, not dose equivalent for a single tissue and radiation type; dividing by the weighting factor would misrepresent the intended scaling; and simply stating energy deposited describes absorbed dose, not dose equivalent.