Radium is a chemical element with the symbol Ra and atomic number 88. Pure radium is silvery-white, but it readily reacts with nitrogen on exposure to air, forming a black surface layer of radium nitride (). All isotopes of radium are highly radioactive, with the most stable isotope being Radium-226.
Radium was discovered by Marie Skłodowska-Curie and Pierre Curie in 1898 from the mineral uraninite (pitchblende). They removed uranium from it and found that the remaining material was still radioactive. Further extraction led to the identification of a new element, which they named radium for its intense radioactivity.
Radium is the heaviest of the alkaline earth metals. It emits alpha radiation, beta radiation, and gamma radiation. When mixed with beryllium, it produces neutrons. A single gram of Radium-226 has an activity of disintegrations per second, a unit defined as the Curie ().
Beyond its traditional uses, radium is a major component of Naturally Occurring Radioactive Material (NORM) in industrial processes. In the oil and gas industry, radium isotopes—particularly Radium-226 and Radium-228—are often co-mingled in produced water and mineral scales. These isotopes are leached from deep geological formations and can accumulate in piping, separators, and storage tanks, posing a significant waste management and worker safety challenge. Radium-228, part of the Thorium decay series, is especially prevalent in environments where thorium-bearing minerals are common.
Historically, radium was used in self-luminous paints for watches and instrument dials. The health hazards became widely known through the "Radium Girls," workers who contracted radiation poisoning. Radium is a "bone-seeker" because it is chemically similar to calcium; when ingested, it settles in the bones and can cause osteosarcoma.