What unit is used to measure radiation exposure?

The unit that is traditionally used to measure radiation exposure in the air is the Roentgen. This unit was specifically developed to quantify the amount of ionization produced in air by X-rays or gamma rays. The Roentgen is defined based on the amount of charge produced by gamma or X-ray radiation in one cubic centimeter of dry air at a specific temperature and pressure.

While the Gray and Sievert are also important in the field of radiation, they serve different purposes. The Gray is used to measure the absorbed dose of radiation in any material, focusing on how much energy is deposited by radiation in a given mass, regardless of the biological effects. The Sievert, on the other hand, is used to measure the biological effect of radiation, taking into account the type of radiation and its potential impact on living tissue. The unit Rad is an older measure of absorbed dose that has largely been replaced by the Gray.

Thus, for measuring general radiation exposure specifically in air, the Roentgen is the correct unit to use.