What is the SI measurement of radiation exposure in air?

The correct measurement of radiation exposure in air in the SI system is the Gray-a (Gy-a). This unit specifically represents the amount of radiation energy deposited in air, making it applicable to situations where radiation exposure needs to be measured. The term 'Gray-a' indicates that the measurement pertains to air, differentiating it from the Gray, which measures the absorbed dose regardless of the medium.

In contrast, the Gray (Gy) is also a measure of energy absorbed, but it does not specify the medium in which the dose is measured, which can lead to confusion in contexts where air exposure is specifically relevant.

The Sievert (Sv) is used to quantify the biological effect of ionizing radiation, providing a context for assessing risk rather than exposure levels directly, thus it does not apply as a direct measure of radiation exposure in air.

The Röntgen (R) is an older unit that measures ionization produced in air by X-rays or gamma rays and is not part of the SI unit system. It is outdated for scientific use in modern contexts despite being historically significant.

Understanding the distinction between these units is essential for comprehending radiation exposure and its implications in medical and environmental contexts.