radium (Ra)

radium atom

Electron shell diagram for radium.

Radium (Ra) is a rare, brilliant-white, luminescent, highly radioactive, metallic element having 16 isotopes (4 of them natural – radium 226, 228, 224, and 223) of which radium 226 (Ra266), with a half-life of 1,622 years is the most common. The gas radon is a decay product. Radium is one of the alkaline earth metals. It has white salts which turn blue as the radium decays, and which emit a blue glow due to ionization of the air by radiation.


Radium was used in cancer radiotherapy (but has been superseded by other radioisotopes, such as cobalt 60) and as a constituent of luminescent paints, and is used as a neutron source for some research purposes. It was discovered in pitchblende (1898) by Pierre and Marie Curie, and first isolated in metallic form by Marie Curie in 1911.


atomic number 88
relative atomic mass 226.025
relative density 5.0
melting point 700°C (1,292°F)
boiling point 1,737°C (3,157°F)