Rad is primarily a measure of what?

• A. The energy deposited or absorbed in a medium
• B. The exposure in air
• C. The rate of disintegration
• D. The biological effect of radiation

Answer: (A)

Rad is a measure of the energy actually deposited in a material per unit mass, i.e., the absorbed dose. It directly reflects how much radiation energy is transferred into tissue or other matter, which is what can cause damage. Exposure in air (measured in roentgens) is a different concept that describes ionization of air, not energy absorbed by a substance. Rate of disintegration (activity) refers to how many decays occur per unit time, not how much energy is absorbed. Biological effect is assessed with dose equivalent (rem or sievert), which weights the absorbed dose by radiation type to estimate harm. So the rad best answers the idea of energy deposited per mass in the material.