A measure of radiation dose based on biological effect is?

• A. RAD
• B. REM
• C. Roentgen
• D. Gray

Answer: (B)

Biological harm is what we’re trying to compare when we talk about radiation dose, so the quantity used is dose equivalent. This takes the energy actually deposited in tissue (the absorbed dose) and adjusts it for how damaging different types of radiation can be. The unit that represents this adjusted, biologically relevant dose historically is the rem (Roentgen Equivalent Man). It effectively multiplies the absorbed dose by a radiation weighting factor to reflect greater or lesser biological impact, giving a single value that relates to potential harm to a person. One rem equals 0.01 sievert, with sievert being the modern SI unit. Other measures shown—Roentgen quantifies exposure in air, not dose to tissue; Gray measures energy deposited (absorbed dose) without regard to biological effectiveness; RAD is an older absorbed-dose unit—do not directly express how harmful the radiation might be. Hence, REM is the best choice for a dose measure based on biological effect.