radium

radium. It is a highly radioactive alkaline earth metal discovered by Marie Curie and Pierre Curie in 1898, isolated from uraninite. All isotopes are unstable, with radium-226 being the most stable and a product of the uranium-238 decay chain. Its intense radioactivity, which causes radioluminescence and the production of radon gas, led to both pioneering medical uses and severe public health scandals.

Properties

Radium is a dense, silvery-white metal that tarnishes rapidly in air, forming a black coating of radium nitride. Chemically, it resembles barium, readily forming the Ra²⁺ ion in compounds like radium chloride and radium sulfate. Its most defining characteristic is extreme radioactivity; it emits alpha particles, beta particles, and gamma rays, and its decay heats its compounds and surrounding materials. This radiation excites phosphors, causing the persistent glow historically seen on watch dials. The element has no stable isotopes, with radium-223 and radium-224 also having medical significance due to their shorter half-lives.

History

The discovery followed Marie Curie's investigation of the radioactivity in pitchblende from Jáchymov, which was more intense than could be explained by its uranium content. After laborious processing, the Curies isolated a new element, naming it for the Latin *radius* (ray). André-Louis Debierne is often credited with the first isolation of metallic radium in 1910 via electrolysis of radium chloride. The early 20th century saw a "radium craze," with the element marketed in quack remedies and consumer products, exemplified by the Radithor scandal. The tragic health outcomes for workers, notably the Radium Girls in New Jersey and Illinois, were pivotal in establishing modern occupational safety standards and workers' compensation laws.

Occurrence and production

Radium occurs naturally only as a decay product in uranium and thorium ores, such as uraninite, carnotite, and autunite, with minute quantities found in all uranium-bearing rocks. It is formed from the decay of thorium-230. Historically, production involved extensive processing of ore residues from uranium mining, primarily in regions like the Czech Republic, the Congo Free State, and Great Bear Lake in Canada. Modern supply comes mainly from the refinement of uranium mill tailings or is generated synthetically as needed. It is no longer mined commercially, with available stocks largely held by agencies like the National Institute of Standards and Technology and the Commissariat à l'énergie atomique.

Applications

Its primary historical use was in self-luminous paint for aircraft instruments, watch dials, and compasses, often using a mixture with zinc sulfide. In medicine, its gamma emissions made it a key radiation source for brachytherapy to treat cancers, a technique pioneered at institutions like the Memorial Sloan Kettering Cancer Center. The use of radium needles and radium plaques was largely superseded by safer isotopes like cobalt-60 and cesium-137 after World War II. Radium was also once used in industrial radiography and as a neutron source when mixed with beryllium. Today, the isotope radium-223 dichloride (Xofigo) is used in targeted alpha therapy for metastatic prostate cancer.

Health effects and safety

Radium is a profound radiological hazard due to its bone-seeking behavior, mimicking calcium and incorporating into the skeleton, where it irradiates bone marrow and can cause osteosarcoma. Internal contamination, as occurred with the Radium Girls who ingested paint by pointing brushes with their lips, leads to radium jaw, severe anemia, and cancers. Its decay produces radon gas, an inhalation risk. Handling requires stringent radiation protection protocols, including shielded containment (often with lead) in facilities like Los Alamos National Laboratory. Its environmental legacy persists at contaminated sites such as Superfund locations in Montclair and West Chicago, requiring extensive remediation.

Category:Chemical elements Category:Alkaline earth metals Category:Radioactive elements