Chemical element, one of the alkali metals, chemical symbol Cs, atomic number 55. The first element discovered by spectroscopy (1860), it is silvery white, liquid at warm room temperature (melting at 83 °F [28.4 °C]), and very soft when solid. About half as abundant as lead, it occurs in minute quantities as ores. It reacts explosively with cold water and is used to scavenge traces of oxygen and other gases in electron tubes. Other uses are as a catalyst and in photoelectric cells, ion propulsion systems, atomic clocks, and plasma for thermoelectric conversion. Cesium salts have various specialty applications, including in mineral waters.
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The emission spectrum of caesium has two bright lines in the blue area of the spectrum along with several other lines in the red, yellow, and green areas. This metal is silvery gold in color and is both soft and ductile. Caesium is the second most electropositive and alkaline of the chemical elements and has the second lowest ionization potential (after francium). Caesium is the least abundant of the five non-radioactive alkali metals (francium is the least common alkali metal, but since it is highly radioactive with an estimated 30 grams in the entire Earth's crust at one time, its abundance can be considered zero in practical terms).
Along with gallium, francium, rubidium, 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 , 157 K).
Caesium hydroxide (CsOH) is a very strong base and will rapidly etch the surface of glass. CsOH is often stated to be the "strongest base", but in fact many compounds such as n-butyllithium and sodium amide are stronger.
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 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 caesium 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 caesium chloride and its nitrate. The price of caesium metal in 1997 was about US$30 per gram, but its compounds are much cheaper. See also Caesium minerals.
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 a large number of isotopes, it has only one naturally occurring stable isotope, 133Cs. Most of the other isotopes have half-lives from a few days to fractions of a second. The radiogenic isotope 137Cs has been used in hydrologic studies, analogous to the use of 3H. 137Cs is produced from the detonation of nuclear weapons and is produced in nuclear power plants, and was released to the atmosphere most notably from the 1986 Chernobyl meltdown. This isotope (137Cs) is one of the numerous products of fission, directly issued from the fission of uranium.
Beginning in 1945 with the commencement of nuclear testing, 137Cs was released into the atmosphere where it is not absorbed readily into solution and is returned to the surface of the earth as a component of radioactive fallout. Once 137Cs 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 cannot be estimated as a function of time. Caesium-137 has a half-life of 30.17 years. It decomposes to barium-137m (a short-lived product of decay) then to a form of nonradioactive barium.
Caesium compounds are rarely encountered by most persons. All caesium compounds should be regarded as mildly toxic because of its chemical similarity to potassium. Large amounts cause hyperirritability and spasms, but such amounts would not ordinarily be encountered in natural sources, so Cs is not a major chemical environmental pollutant. Rats fed caesium in place of potassium in their diet die, so this element cannot replace potassium in function.
The isotopes 134Cs and 137Cs (present in the biosphere in small amounts as a result of radiation leaks) represent a radioactivity burden which varies depending on location. Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium), which are actively accumulated by the body.
A comparison using the caesium-137 technique of the relative importance of cultivation and overland flow on soil erosion in a steep semi-tropical sub-catchment.
Mar 01, 2001; Introduction Soil erosion is a major environmental concern in agricultural practice, especially on steeply sloping land. In...
Caesium theft puzzle: scrap or dirty bomb? Questions abound over what four men arrested at a Pretoria garage were doing with radioactive matter.(News)
Jul 23, 2010; So were the four guys whom the police caught at a Garsfontein, Pretoria, garage on July 9 trying to sell a container of...
Big terror deal or plumber's scrap? Radioactive caesium-137 bust could explode the al-Qaeda dirty bomb story.(News)
Jul 23, 2010; BYLINE: PETER FABRICIUS So were the four guys whom the police caught at a Garsfontein, Pretoria, garage on July 9 for trying to...