What is roentgens?

Roentgen is a unit of measurement for exposure to ionizing radiation, specifically X-rays and gamma rays. It quantifies the amount of radiation that produces a certain amount of ionization in air, defined as 2.58 x 10^-4 coulombs per kilogram of air. The unit is named after Wilhelm Conrad Röntgen, who discovered X-rays in 1895. While still used in some contexts, the roentgen has largely been replaced by more precise units like the gray and sievert in modern radiation measurement.