Radium

Radium is the radioactive alkaline earth metal discovered by Marie and Pierre Curie in 1898. Glowing faintly blue in the dark from its own radioactivity, it was once used in luminous paint for clock dials and instrument panels, with tragic consequences for the workers who applied it. Marie Curie won two Nobel Prizes partly for this discovery.

• Atomic Number8888 protons, 88 electrons
• Atomic Mass226.02541 u88× heavier than hydrogen
• State at Room TempSolidSolid
• Density5 g/cm³
• Melting / Boiling699.9°C / 1139.8°C
• Discovered1898

What is Radium?

Radium is an alkaline earth metal with 88 protons and no stable isotopes. Radium-226 has the longest half-life (1,600 years) and is the most common. It is produced by the decay of uranium-238 and itself decays through a chain of radioactive daughters including radon, polonium and ultimately lead. The faint blue glow of radium compounds comes from radioactivity exciting the air and chemical compounds around it.

Named from the Latin radius meaning ray, because of its continuous radiation. Discovered in 1898 by Marie and Pierre Curie while processing tonnes of uranium ore (pitchblende) in Paris. They identified two new radioactive elements, polonium and radium. Marie Curie won Nobel Prizes in both Physics (1903) and Chemistry (1911).

Fact The Radium Girls, young women who painted luminous watch dials with radium paint in the 1920s in the USA, were encouraged to point their brushes by licking them. They suffered horrific radiation poisoning including jaw necrosis and cancers. Their lawsuits against the Radium Luminous Material Corporation established workers' rights to sue employers for industrial disease.

Where you find Radium

On Earth

Radium occurs naturally in uranium and thorium ores as a decay product. It is one of the rarest naturally occurring elements, only approx. 1 gram of radium per 7 tonnes of uranium ore.

• Uranium ores. Radium occurs as a decay product in all uranium and thorium ores worldwide. Extraction requires processing enormous quantities of ore for tiny yields.

How we use Radium

• Cancer radiotherapy (historical).. Radium was the first radioactive element used to treat cancer. Radium-222 gas (radon) sealed in tiny gold needles was implanted near tumours. Now replaced by safer isotopes.
• Luminous paint (historical).. Radium mixed with zinc sulfide phosphor produced self-luminous paint used on watch and instrument dials. The Radium Girls, factory workers who painted dials, suffered severe radiation poisoning.

Did you know? Marie Curie's notebooks are still too radioactive to handle safely, they are stored in lead-lined boxes in the Bibliothèque nationale de France and anyone wishing to read them must sign a waiver and wear protective gear. Marie Curie died of aplastic anaemia in 1934, almost certainly caused by decades of radiation exposure.

How it was discovered

Discovered in 1898 by Marie and Pierre Curie while processing several tonnes of pitchblende. By concentrating the radioactive material through many stages of chemical processing, they eventually isolated radium in a pure enough form to measure its atomic weight. The discovery won them the 1903 Nobel Prize in Physics (shared with Becquerel). Marie Curie received a second Nobel (Chemistry, 1911) for discovering polonium and radium.

Deeper dive: radium properties and applications

Radium was once thought to be a miraculous health tonic. "Radium water", water left in contact with radium ore, was sold as a health drink. Eben Byers, an American socialite, drank a bottle of radium-laced water every day for years and promoted it enthusiastically until his jaw and skull began to dissolve from radiation necrosis. His case, publicised in a 1932 Wall Street Journal article headlined "The Radium Water Worked Fine Until His Jaw Fell Off", helped end the radium health fad.

Moving to 89 protons on the periodic table brings us to Francium.