In 1915, Curie’s radium emanation in hollow needles was later identified as radon gas.
The material was initially known as “radium emanation,” an old name for the radioactive gas released by radium compounds. Marie Curie prepared hollow needles containing the emanation for medical use, including attempts to sterilize infected tissue during the First World War.
Radon is a radioactive noble gas produced in the decay chain of radium, which itself occurs in the uranium-238 decay series. Because it is chemically inert and gaseous, radon could be collected and placed in small containers or needles for early forms of radiation treatment.
The terminology developed gradually. Friedrich Ernst Dorn reported radium’s radioactive emanation in 1900, while the name “radon” was adopted only later, becoming part of a broader naming system for radioactive gases. Thus, “radium emanation” describes the historical substance and “radon” is the modern chemical identification—not neon, helium, or argon.