What does the roentgen measure?

The roentgen is a unit of measurement specifically used to quantify exposure to ionizing radiation in the air. It measures the amount of ionization produced in air by gamma rays or X-rays, reflecting the radiation's strength and its potential to cause ionization in the surrounding air. The measurement of exposure is crucial in fields such as radiology and radiation therapy, where understanding the levels of radiation is essential for ensuring safety and effectiveness.

In contrast, absorbed dose refers to the amount of energy deposited by radiation in a material, typically expressed in grays (Gy). Absorbed dose equivalent involves a measurement that accounts for the biological effect of different types of radiation, and it is expressed in sieverts (Sv). Energy equivalent, while relevant to physics, is not a standard measure used specifically for ionizing radiation exposure. Thus, the roentgen's primary focus on exposure makes it the accurate answer to the question.