Caesium: a metal used to check clocks
The first element discovered by spectral analysis
This element is a soft, silvery-gold metal with a low melting temperature - 28.7°С (I.e. a little over room temperature).
The reactive ability of the elements in the group increases from top to bottom. Caesium is at the bottom of the first group, and is very reactive. If you throw a little caesium into water, a powerful explosion takes place, and the metal burns quickly in air. It is only possible to work with it in an inert atmosphere, and it must be stored under a layer of oil, or in sealed capsules. Caesium has two radioactive isotopes – Cs-134 and Cs-137.
Occurrence of caesium
Caesium received its name from the Latin word caesius, “sky-blue”. Caesium is contained in the rare mineral pollucite. Its deposits are mainly found in Canada, and also in Namibia, Zimbabwe, Russia (Kola Peninsula, Eastern Sayan, Transbaikal region). Small, economically insignificant deposits of pollucite are also found in Kazakhstan, Mongolia and Italy. Around 20 tons of enriched caesium ore is produced worldwide annually. The annual volume of production of the pure metal is around 9 tons. The demand for caesium is constantly growing, and exceeds the volumes of its production. So the situation of the caesium market is highly precarious, just as it is with tantalum and rhenium.
How caesium was discovered
In 1860, the German scientists Robert Wilhelm Bunsen and Gustav Robert Kirchhof were studying the waters of the Bad Dürkheim mineral spring by the method of optic spectroscopy. They detected two new blue lines in the spectrum. Thus, caesium became the first element to be discovered by spectral analysis! In 1882, the Swedish chemist Carl Setterberg conducted electrolysis of an alloy of caesium cyanide and barium and extracted caesium in pure form.
Caesium-137 has a half-life of 30 years. This infamous isotope was present in radioactive waste from underground nuclear testing (1945-1963), and also in the fallout from the Chernobyl disaster. Large quantities of Cs-137 were detected from Eastern Europe to Ireland. It affected plants and livestock grazing on contaminated lands. The use of these areas was highly restricted, and plants and animals were tested for contamination. Traces of the isotope were still detected even 25 years after the disaster.
Areas were also contaminated by Cs-137 in Japan after the disaster at the nuclear energy plant in Fukushima in 2011. Fortunately, according to numerous researchers, the radioactive particles settled in processed fuel, and were not carried away with the smoke, stopping them from spreading too far.
Caesium is a microelement contained in plants and the organisms of animals (mainly in the muscles, heart, liver and blood). Radioactive Cs-137 accumulates in freshwater algae, arctic plants and lichens. A relatively high accumulation ratio is noted in reindeer and North American water birds. The following mushrooms are also considered to be “accumulators” of radioactive caesium: yellow boletus, boletus, paxil, woolly milkcap and bay bolete. But the biological role of caesium is still not fully understood.
The stable isotope Cs-133 is used in photoelements, photomultipliers and detectors of ionizing radiation (caesium iodide). Cs-133 is also used as an optical material (in the form of iodide and bromide), and in the manufacture of luminous tubes (in combinations with zirconium and tin). Caesium acts as a catalyst in the production of ammonium, sulfuric acid, butyl alcohol, in dehydrogenization reactions and in the production of formic acid. Caesium is the basis of medical products for the treatment of ulcerous diseases, diphtheria, shocks and schizophrenia. Caesium plasma is a component of MHD-generators with high power efficiency.
Cs-133 is used in atomic clocks – the most precise devices for telling the time. Since 1967, in the SI international system of units, 1 second has been defined as 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. The first caesium atomic clock was built in 1955 by Louis Essen at the National Physics Laboratory in the UK. This clock has an accuracy of one second in 300,000 years. Today, atomic clocks are used in the navigation systems of spacecraft, satellites, ballistic rockets, aircraft, submarines and automobiles functioning automatically by satellite link. Atomic clocks are also used in systems of satellite and ground telecommunications, in mobile base stations, international and national standards offices and services of exact time.