Which statement best describes absorbed dose versus dose equivalent?

• A. The rate of exposure of air
• B. The total energy emitted by the source
• C. The energy imparted by ionizing radiation per unit mass of tissue
• D. The energy imparted per unit time in the beam

Answer: (C)

Absorbed dose is defined as the energy deposited by ionizing radiation in a unit mass of tissue, and it is expressed in grays (1 Gy = 1 J/kg). This quantity focuses on how much energy actually gets into the tissue, regardless of how damaging that energy may be. Dose equivalent, on the other hand, takes that absorbed energy and adjusts it for the biological effect by multiplying by a radiation weighting factor, giving units of sieverts. In other words, absorbed dose tells you how much energy is deposited, while dose equivalent reflects the potential for biological harm from that energy, depending on the type of radiation.

The statement describing energy imparted by ionizing radiation per unit mass of tissue captures the essence of absorbed dose. The other options point to exposure in air, the total energy emitted by the source, or the energy deposited per unit time (dose rate), none of which define absorbed dose (or dose equivalent) directly.