What unit is used to measure exposure?

• A. Gray (Gy)
• B. Sievert (Sv)
• C. Coulombs per kilogram (c/kg)
• D. Becquerel (Bq)

Answer: (C)

Exposure is about the amount of ionization radiation produces in air. In SI units, that quantity is expressed as Coulombs of charge produced per kilogram of air, written as C/kg. An ionization chamber collects the charge created by ion pairs in a known mass of air, and the resulting current is proportional to the exposure, linking the physical ionization to a measurable charge per mass.

The other units measure related but different things: the gray (Gy) measures energy deposited per kilogram (absorbed dose) in any material, the sievert (Sv) accounts for biological effect by applying radiation weighting, and the becquerel (Bq) measures how many radioactive decays occur per second (activity). Since exposure specifically quantifies ionization in air, C/kg is the appropriate unit.