What are the SI units for absorbed dose and for equivalent dose in radiation protection?

• A. Gray (Gy) for absorbed dose; Sievert (Sv) for equivalent dose
• B. Joule (J) for absorbed dose; Becquerel (Bq) for equivalent dose
• C. Newton (N) for absorbed dose; Pascal (Pa) for equivalent dose
• D. Coulomb (C) for absorbed dose; Volt (V) for equivalent dose

Answer: (A)

Absorbed dose is about how much energy from radiation is deposited in a target mass. In SI units this is gray (Gy), defined as 1 joule of energy deposited per kilogram of material (1 Gy = 1 J/kg). The equivalent dose then relates that energy deposition to the biological harm it can cause, by applying a radiation weighting factor that depends on the type of radiation. The unit for this protective quantity is the sievert (Sv), which is defined as 1 Gy multiplied by the appropriate weighting factor (Sv = Gy × WR). For many common radiations like X-rays and gamma rays, WR is 1, so 1 Gy corresponds to 1 Sv in terms of risk, while for alpha particles WR is higher (about 20), making 0.1 Gy equal to 2 Sv in terms of potential harm. Other listed units (joule, becquerel, newton, pascal, coulomb, volt) are not used for dose or protective risk.