The unit rem is used to express which of the following?

• A. The energy absorbed per kilogram
• B. The dose to a specific organ
• C. The rate of decay
• D. Measured radiation exposure in people

Answer: (D)

Rem expresses the dose equivalent a person receives from radiation, factoring in the different biological effects of various radiations. It’s not a measure of energy deposited per kilogram (that’s absorbed dose, in gray), nor a measure of how fast the material decays (that’s activity, in becquerels), and it isn’t simply a specific organ dose without considering tissue sensitivity. Historically, rem, short for roentgen equivalent man, was used to express how much radiation exposure a person would effectively experience, with sievert now serving as the modern equivalent unit.