Where was radon first recognized as a distinct chemical element?

Radon was recognized as a distinct radioactive gas in the early 20th century through research in Germany and Austria. Scientists such as Friedrich Ernst Dorn showed that a gaseous product was emitted from radium, and later studies established it as a new element. Because it is radioactive and part of the uranium decay chain, radon occurs naturally in rocks and soil. Its discovery mattered not only for chemistry but also for public health, because radon can accumulate in buildings.