The unit of exposure in air is:

The unit of exposure in air is:

• A. Gray (Gy)
• B. Sievert (Sv)
• C. Coulomb per kilogram
• D. Roentgen (R)

Answer: (D)

Exposure in air is about the ionization produced by radiation in air. The Roentgen is defined as the exposure that creates a specific amount of charge per mass of air (2.58×10^-4 C/kg) under standard conditions, so it directly quantifies ionization in air. That makes it the unit used for exposure in air. Gray measures energy deposited in tissue (absorbed dose), and Sievert accounts for biological effect (dose equivalent), neither of which describe ionization in air. The Coulomb per kilogram is the SI unit for exposure, but historically and in many radiography contexts, roentgen is the unit associated with exposure in air.

Exposure in air is about the ionization produced by radiation in air. The Roentgen is defined as the exposure that creates a specific amount of charge per mass of air (2.58×10^-4 C/kg) under standard conditions, so it directly quantifies ionization in air. That makes it the unit used for exposure in air. Gray measures energy deposited in tissue (absorbed dose), and Sievert accounts for biological effect (dose equivalent), neither of which describe ionization in air. The Coulomb per kilogram is the SI unit for exposure, but historically and in many radiography contexts, roentgen is the unit associated with exposure in air.