Caesium: Encyclopedia - Caesium

Caesium

Caesium (cesium in the United States) pronounced /ˈsiːziəm/; is a chemical element in the periodic table that has the symbol Cs and atomic number 55. It is a soft silvery-gold alkali metal which is one of at least three metals that are liquid at or near room temperature. This element is most notably used in atomic clocks.

The variant spelling cesium is sometimes used, especially in North American English, but caesium is the spelling used by the IUPAC, although since 1993 it has recognized cesium as a variant as well.

Caesium - Notable characteristics

The electromagnetic spectrum of caesium has two bright lines in the blue part of the spectrum along with several other lines in the red, yellow, and green. This metal is silvery gold in color and is both soft and ductile. Caesium is also the most electropositive and most alkaline of the stable chemical elements and also has the least ionization potential of all the elements, except for francium. Caesium is the least abundant of the five non-radioactive alkali metals. (Technically, francium is the least common alkali metal, but since it is highly radioactive with less than 30 grams in the entire earth at one time, its abundance can be considered zero in practical terms.)

Along with gallium and mercury, caesium is among the only metals that are liquid at or near room temperature. Caesium reacts explosively in cold water and also reacts with ice at temperatures above −116°C. Caesium hydroxide (CsOH) is a very strong base and will rapidly etch the surface of glass.

Caesium - Applications

Caesium is most notably used in atomic clocks, which are accurate to seconds in many thousands of years. Since 1967, the International System of Measurements bases its unit of time, the second, on the properties of caesium. SI defines the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the caesium-133 atom.

• Cs-134 has been used in hydrology as a measure of caesium output by the nuclear power industry. This isotope is used because, while it is less prevalent than either Cs-133 or Cs-137, Cs-134 can be produced solely by nuclear reactions. Cs-135 has also been used in this function.
• Like other group 1 elements, caesium has a great affinity for oxygen and is used as a "getter" in vacuum tubes.
• This metal is also used in photoelectric cells.
• In addition, caesium is used as a catalyst in the hydrogenation of certain organic compounds.
• Radioactive isotopes of caesium are used in the medical field to treat certain types of cancer.
• Caesium fluoride is widely used in organic chemistry as a base and as a source of anhydrous fluoride ion.
• Caesium vapor is used in many common magnetometers.
• Because of their high density, Caesium chloride solutions are commonly used in molecular biology for density gradient ultracentrifugation, primarily for the isolation of nucleic acids from biological samples.

More recently this metal has been used in ion propulsion systems.

Caesium - History

Caesium (Latin caesius meaning "sky blue") was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water from Dürkheim, Germany. Its identification was based upon the bright blue lines in its spectrum and it was the first element discovered by spectrum analysis. The first caesium metal was produced in 1881. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical applications.

Caesium - Occurrence

An alkali metal, caesium occurs in lepidolite, pollucite (hydrated silicate of aluminium and caesium) and within other sources. One of the world's most significant and rich sources of this metal is located at Bernic Lake in Manitoba. The deposits there are estimated to contain 300,000 metric tons of pollucite at an average of 20% caesium.

It can be isolated by electrolysis of fused cyanide and in a number of other ways. Exceptionally pure and gas-free caesium can be made by the thermal decomposition of caesium azide. The primary compounds of caesium are its chloride and its nitrate. The price of caesium in 1997 was about $US 30 per gram.

Caesium - Isotopes

Caesium has at least 39 known isotopes which is more than any other element, except francium. The atomic masses of these isotopes range from 112 to 151. Even though this element has the largest number of isotopes, it has only one naturally occurring stable isotope, Cs-133, the other isotopes (except for the isotopes noted on this page) have half-lives from a few days to fractions of a second. The radiogenic isotope Cs-137 has been used in hydrologic studies, analogous to the use of H-3 (tritium). Cs-137 is produced from the detonation of nuclear weapons and is produced in nuclear power plants, and notably from the 1986 Chernobyl meltdown. Beginning in 1954 with the commencement of nuclear testing, Cs-137 was released into the atmosphere where it is absorbed readily into solution. Once Cs-137 enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport. As a result, the input function of these isotopes can be estimated as a function of time.

Caesium - Precautions

All alkaline metals are highly reactive. Caesium, being one of the heavier alkaline metals, is also one of the most reactive and is highly explosive in cold water. Caesium should be considered highly toxic. Some of its radioisotopes are even more toxic. Caesium hydroxide is an extremely strong base, and can attack glass.

See also

• Cs-137
• Goiânia accident - a major radioactive contamination incident involving a small rod of caesium chloride.

Adapted from the Wikipedia article "Caesium", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki