What is the radiation protection quantity measured as the energy absorbed in matter?

• A. Absorbed Dose
• B. Dose Equivalent
• C. Effective Dose
• D. Exposure

Answer: (A)

Energy deposited per unit mass of matter by ionizing radiation is the absorbed dose. This physical quantity directly quantifies how much energy the material absorbs, independent of the type of radiation or biological effects. The SI unit is the gray (Gy), which is joules per kilogram.

Dose equivalent and effective dose are derived from absorbed dose. They incorporate factors for radiation quality and tissue sensitivity to reflect biological risk, so they go beyond the purely physical energy deposited. Exposure, on the other hand, measures ionization in air (not energy absorbed in matter) and uses different units, making it unsuitable for describing energy deposition in material.