In what medium is roentgen (R) exposure primarily measured?

Roentgen (R) exposure is primarily measured in air because it quantifies the amount of ionization produced by X-rays or gamma rays in a specific volume of air. This measurement is based on the principle that the ionization of air molecules reflects the potential to cause biological effects in human tissue.

By convention, the roentgen is defined through the amount of radiation that produces a certain amount of ionization in air, making it a practical choice for radiation safety monitoring. This measurement is particularly useful in environments where ionizing radiation may be present, allowing for accurate assessments of exposure levels.

While other media such as water, solid materials, and vacuum can interact with ionizing radiation, they are not used as a standard measure for roentgen exposure. Understanding this distinction is crucial for effective radiation protection and safety practices.