Barium Ba

Discovery

In the early seventeenth century Vincenzo Casciarolo, a shoemaker and alchemist in Bologna, found that a stone collected on a nearby mountain glowed in the dark after being roasted. This "Bologna stone" was baryte (barium sulfate), and it became an early subject in the study of phosphorescence.

In 1774 Carl Wilhelm Scheele showed that the oxide in baryte, called baryta, differed from lime. Humphry Davy isolated barium metal by electrolysis in 1808.

In 1938 Otto Hahn and Fritz Strassmann in Germany bombarded uranium with neutrons and, to their surprise, identified much lighter barium among the products. Lise Meitner and Otto Frisch interpreted this as the splitting of the uranium nucleus, which they called fission.

Origin of the name

The name comes from the Greek barys, "heavy", originally referring to the dense mineral baryte. Ironically the metal itself, with a density of about 3.6 g/cm³, is not particularly heavy. The symbol is Ba.

Main uses

• Drilling mud: finely ground baryte adds weight to drilling mud, holding back high-pressure gas and oil underground. This accounts for most barium mineral consumption.
• Medical imaging: barium sulfate blocks X-rays and outlines the oesophagus, stomach and intestines in contrast studies.
• Fireworks: barium nitrate produces green flames.
• Electronic ceramics: barium titanate is the dielectric in multilayer ceramic capacitors, hundreds to thousands of which sit inside a single smartphone.
• Other: barium ferrite magnets, getters in vacuum tubes and special glasses.

Isotopes

Natural barium has seven isotopes, barium-130, -132, -134, -135, -136, -137 and -138, with barium-138 making up about 72%. Barium-130 decays so slowly that it is effectively stable. When caesium-137 decays, it forms excited barium-137m (half-life about 2.6 minutes), and the 662 keV gamma ray this emits is what is usually called "the caesium-137 gamma ray". Barium-133, with a half-life of about 10.5 years, is used to calibrate radiation detectors.

In everyday life

Whether a barium compound is dangerous depends on whether it dissolves. Barium sulfate is practically insoluble in water and stomach acid, so it passes through the body without being absorbed and is safe as a contrast agent. Soluble compounds such as barium carbonate and barium chloride, however, are toxic to muscles and the heart; barium carbonate has even been used as rat poison.

After a barium study, patients are usually advised to drink plenty of fluids so that the contrast agent does not harden in the bowel.