Rubidium Rb

Discovery

Rubidium was the second element found by spectroscopy. In 1860 Robert Bunsen and Gustav Kirchhoff in Heidelberg used their new spectroscope, which split the light from a flame into its component colours, to discover caesium.

In 1861 they turned the same technique on the mineral lepidolite and saw deep red spectral lines that matched no known element. Bunsen went on to prepare rubidium compounds and to obtain a nearly metallic sample.

More than a century later rubidium returned to the spotlight. In 1995 Eric Cornell and Carl Wieman cooled a gas of rubidium-87 atoms to within a whisker of absolute zero and produced the first Bose–Einstein condensate, a new state of matter. They shared the 2001 Nobel Prize in Physics with Wolfgang Ketterle.

Origin of the name

The name comes from the Latin rubidus, "deep red", after the vivid red lines in its spectrum. The symbol is Rb, and the word shares its root with the gemstone ruby.

Main uses

• Atomic clocks: rubidium frequency standards are compact and relatively inexpensive, so they are used in telecommunications networks, broadcasting and navigation satellites.
• Physics research: rubidium is easy to laser-cool and is one of the most common atoms in atom interferometers, quantum simulators and Bose–Einstein condensate experiments.
• Medicine: rubidium-82 is used in PET scans that measure blood flow to the heart muscle.
• Other: small amounts go into photocells, special glasses and vapour-cell magnetometers.

Isotopes

Natural rubidium is a mixture of stable rubidium-85 (about 72%) and radioactive rubidium-87 (about 28%). Rubidium-87 has a half-life of roughly 49 billion years, longer than the age of the universe, and beta-decays to strontium-87. Measuring this pair is the basis of rubidium–strontium dating, a classic method for determining the ages of old rocks and meteorites. Medical rubidium-82 has a half-life of only about 75 seconds and is eluted from a strontium-82 generator right before a scan.

In everyday life

Rubidium rarely forms minerals of its own. It occurs alongside potassium and caesium in minerals such as lepidolite and pollucite and is recovered as a by-product of lithium and caesium production. It is surprisingly common in Earth's crust, roughly comparable to copper or zinc.

The body handles rubidium much like potassium, taking it into cells, so everyone carries a trace of it, though it is not considered essential. The metal is stored in sealed glass ampoules or under oil, because contact with water releases hydrogen with explosive violence.