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

In recent years, the Navy has recovered radioactive objects, including dials and deck markers coated with paint containing Radium isotopes to provide a glow-in-the-dark effect.

From Los Angeles Times • Nov. 7, 2025

"Radium is naturally radioactive, with a short lifetime and we can currently only produce radium monofluoride molecules in tiny quantities," says study lead author Shane Wilkins, a former postdoc at MIT.

From Science Daily • Oct. 26, 2025

Only 25 minutes south of Radium, the Fairmont Hot Springs Resort pools are Canada’s largest natural mineral hot springs.

From Seattle Times • Mar. 23, 2024

The targeted building, the Pavillon des Sources, was one of three constructed when the Radium Institute, now known as the Curie Institute, was established in 1909.

From Science Magazine • Jan. 10, 2024

In 1947, delivering the annual Janeway Lecture of the American Radium Society, he reported that of his original 252 patients, only 18 were still alive less than ten years after the experiment.

From "Big Science" by Michael Hiltzik