What does the Roentgen measure?

The Roentgen measures the amount of ionization produced in air by X-ray and gamma radiation. It specifically quantifies the charge produced in a volume of air due to ionizing radiation, thus providing a direct assessment of the exposure level to ionizing radiation. This measurement is important because it helps gauge the amount of radiation that people may be exposed to in environments such as medical imaging facilities or nuclear industries, where X-rays and gamma rays are commonly present.

In contrast, other measures such as absorbed dose assess the energy deposited in tissue, rather than in air, while dose equivalent takes into account the biological effects of different types of radiation, and exposure time is simply the duration of radiation exposure without relating it to a specific measurement of ionization. Therefore, the correct answer focuses specifically on the concept of ionization in air, which is the fundamental aspect that the Roentgen is designed to measure.