radium

American  

[rey-dee-uhm] / ˈreɪ di əm /

noun

1. Chemistry. a highly radioactive metallic element whose decay yields radon gas and alpha rays. Ra; 226; 88.

2. a lustrous rayon or silk fabric constructed in plain weave and used in women's apparel, lining, and drapery.

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radium British  

/ ˈreɪdɪəm /

noun

1. 1. a highly radioactive luminescent white element of the alkaline earth group of metals. It occurs in pitchblende, carnotite, and other uranium ores, and is used in radiotherapy and in luminous paints. Symbol: Ra; atomic no: 88; half-life of most stable isotope, ²²⁶ Ra: 1620 years; valency: 2; relative density: 5; melting pt: 700°C; boiling pt: 1140°C

   2. ( as modifier )

      radium needle

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radium Scientific  

/ rā′dē-əm /

1. A rare, bright-white, highly radioactive element of the alkaline-earth group. It occurs naturally in very small amounts in ores and minerals containing uranium, and it is naturally luminescent. Radium is used as a source of radon gas for the treatment of disease and as a neutron source for scientific research. Its most stable isotope is Ra 226 with a half-life of 1,622 years. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2.

2. See Periodic Table

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radium Cultural  

1. A naturally occurring radioactive chemical element. Its symbol is Ra.

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Discover More

Radium was discovered by the chemists Marie and Pierre Curie.

Etymology

Origin of radium

1895–1900; < New Latin, equivalent to Latin rad ( ius ) ray ( see radius) + -ium -ium

Explanation

Radium is an element, a highly radioactive metal. Once commonly used to paint glow-in-the-dark watch faces, radium is now known to be extremely toxic. Radium, which was discovered in 1898 by the scientist Marie Curie and her husband Pierre, is one of the rare metals that's radioactive. It's the heaviest element of its type, the alkaline-earth metals, and it is contained within uranium ore. In addition to watches and clocks, radium was used in the past to treat cancer. Today its main use is industrial, in giant x-ray devices that scan for flaws in metal machines.

Example Sentences

But then, he predicted that industries would start using uranium and radium, and pretty soon we’d have … radioactive smog.

From Los Angeles Times • Mar. 26, 2026

Working with radium monofluoride, the researchers tracked the energies of the radium atom's electrons as they moved within the molecule.

From Science Daily • Oct. 26, 2025

Such effects could appear within the nuclei of certain atoms, including radium.

From Science Daily • Oct. 26, 2025

It contains radium that decays into radon gas, which is radioactive and can cause cancer.

From Barron's • Oct. 10, 2025

The cancer was easy to keep secret, because she only had to go back to Hopkins once, for a checkup and a second radium treatment.

From "The Immortal Life of Henrietta Lacks" by Rebecca Skloot