How is exposure to X-rays measured?

Exposure to X-rays is measured in terms of milliroentgens, which is a subunit of the roentgen. The roentgen is used to quantify the amount of X-ray or gamma radiation exposure in terms of ionization produced in air. It specifically measures the ionization in air caused by X-ray or gamma radiation and serves as a practical unit for direct measurement of radiation in medical and screening settings.

Milliroentgens are particularly useful in the context of diagnostic radiology, where the measurements are critical for ensuring patient safety and controlling exposure levels. It allows practitioners to understand and monitor the amount of radiation a patient or worker may receive during procedures involving X-ray imaging.

In contrast, other units mentioned serve different purposes: coulombs per kilogram is more related to the measurement of charge from ionization in a specified mass of air; rems are used to express the biological effects of radiation (dose equivalent) considering the type of radiation; and grays measure absorbed dose, defined as the amount of radiation energy deposited per unit mass of tissue, rather than exposure in air. Thus, for direct measurements of exposure to X-rays, milliroentgens is the appropriate and correct unit to use.