We continue to review some of the most important materials in heat treatment and metallurgy.
Radium (chemical symbol: Ra)
Radium is a soft, shiny, silvery-white metal (Fig. 1) that is highly radioactive. Radium is about 1 million times more radioactive than uranium. It is formed when uranium and thorium radioactively break down in the environment. Radium is extracted from pitchblende, a uranium-rich mineral and ore (UO2). Pitchblende contains a small amount of radium as a radioactive decay product of uranium. In the past, radium was a common element used in many everyday products and was thought to have curative properties until its intense radioactivity was found to cause adverse health effects.
Radium was first discovered by Marie and Pierre Curie in Paris during their study of pitchblende in 1898. After removing the uranium from the ore, they discovered that the remnants were still radioactive. Marie and Pierre Curie further separated these remains to find barium as well as the presence of an unknown element. They named the new element for the Latin word “radius,” meaning “ray,” because of its high radiation emittance. The Curies were able to extract about 1 mg of radium from almost 10 tons of pitchblende. Furthermore, metallic radium was first isolated in 1910 by Marie Curie and Andrew Debierne via electrolysis of radium chloride (RaCl2), the first radium compound isolated in a pure state.
Due to its very high radioactivity, radium has very limited uses. In the past, radium was used in luminous paints in products such as clocks or watch dials (since the radioactive alpha rays could not pass through the glass or metal casings of the watch). This application is considered too hazardous for modern times and is no longer used. Today, radium is used in the radiography of metals, and it can be combined with other metals as a neutron source for research and radiation instrument calibration. The isotope radium-223 is sometimes used in cancer treatments that have spread to bone tissue.
Here are a few important facts about radium.[2,5]
- Atomic number: 88
- Atomic weight: 226
- Melting point: 973 K (700°C or 1292°F)
- Boiling point: 1413 K (1140°C or 2084°F)
- Density: 5 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
- Period number: 7
- Group number: 2
- Group name: Alkaline Earth Metal
- Electron configuration: [Rn] 7s2