Which statement correctly contrasts exposure and absorbed dose and their measurement?

• A. They are identical concepts.
• B. Exposure measures energy deposited per mass; absorbed dose measures ionization in air.
• C. Exposure (air ionization) is measured in coulombs/kg or Roentgen; absorbed dose (Gy) is energy deposited per mass.
• D. Exposure is energy deposition; absorbed dose is particle count.

Answer: (C)

Exposure is about the ionization produced in air by radiation, while absorbed dose is about the energy actually deposited in matter. This makes the units and meaning different: exposure is measured in coulombs per kilogram (or the old Roentgen), reflecting air ionization. Absorbed dose is measured in grays, with 1 Gy equal to 1 joule of energy deposited per kilogram of material. The statement that correctly contrasts them uses exposure units tied to ionization in air and absorbed dose units tied to energy deposition per mass, which is why it’s the best fit. The other ideas mix up what each quantity measures—exposure is not energy deposition, and absorbed dose is not simply a count of particles.