Which unit is used to express the commonly cited occupational dose limits?

• A. Grays (Gy)
• B. Rads
• C. Sieverts (Sv)
• D. Millisieverts (mSv)

Answer: (D)

Occupational dose limits are expressed in a unit that reflects biological risk, not just energy deposited. This is the sievert, which combines the absorbed dose with a radiation quality factor to account for how different types of radiation affect tissue. In practice, limits are given in millisieverts per year because the acceptable exposure levels are relatively small. The gray measures energy deposited (1 Gy = 1 J/kg) and rad is an older absorbed-dose unit; they do not directly convey risk. Since we want to compare risk across radiation types, millisieverts provide the practical, standardized way to express typical occupational limits.