Which statement correctly differentiates exposure from absorbed dose?

• A. Exposure relates to ionization in air; absorbed dose relates to energy deposited in tissue
• B. Exposure measures energy deposited in tissue; absorbed dose measures ionization in air
• C. They are identical quantities
• D. Exposure is measured in Sv and absorbed dose in Gy

Answer: (A)

Exposure measures the ionization produced in air by radiation, while absorbed dose measures the energy actually deposited in a material (such as tissue) per unit mass. This is why the correct statement says exposure relates to ionization in air and absorbed dose relates to energy deposited in tissue. In practical terms, exposure is tied to how much ionization radiation causes in air (historically in units like roentgens or coulombs per kilogram), whereas absorbed dose is about how much energy the tissue absorbs (measured in grays, J/kg). The dose equivalent (sieverts) is a separate concept that accounts for biological effect, not exposure itself. The other options either reverse the quantities, claim they are identical, or mix up the units, which obscures the fundamental difference between ionization in air and energy deposited in matter.