LYCOS RETRIEVER 
Caesium
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Caesium is a soft metal which is often liquid at room temperature due to its relatively low melting point (28.5°C). It is an extremely reactive metal, reacting violently in contact with water and being rapidly attacked in air. As with other alkaline group metals, caesium can be prepared by electrolysis of the fused halides but, in addition, it can ... be prepared by heating the chloride with calcium and distilling out the molten metal. As a photosensitor, caesium has a peak response at 800nm in the infrared, both thermal- and photo-emission being high. Alloys of caesium with antimony, gallium, indium and thorium are generally photosensitive. Caesium is also used in atomic clocks, a standard measure of time, based on the caesium ion resonance of 9,192,631,770 Hz.
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Caesium –137 is the isotope that has caused most problems in the ecological system as a result of Chernobyl. It can easily be absorbed in the nourishment chain because of its chemical characteristics. The caesium – 137 will not disappear in a foreseeable time, as the half-life is 30 years. Therefore, it’s very important to make control measurements of animals and vegetables that form part of the human diet.
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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.
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Caesium (Cs) is taken up across the plasma membrane of root cells through K transporters. Initial investigations revealed that intracellular competition of Cs for K-binding sites on essential proteins is the mechanism of Cs toxicity in plants. To determine which transporters mediate Cs entry, Arabidopsis mutants lacking specific K transporters were generated and their accumulation of Cs compared to wildtype plants. Several mutants lacking CNGCs, (non-selective cyclic-nucleotide gated cation channels) had significantly different shoot Cs concentrations and tolerance to both external and internal Cs, when compared to wildtype. Cs fluxes in the xylem and phloem of wildtype plants and mutants with altered shoot Cs concentrations differed. Transcriptional profiling revealed that the complement of Cs-transporting proteins changed with external ionic conditions, and that in K-deficient plants Cs is likely to be transported by high affinity K transporters (KUPs).
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Caesium ranks about 46th in natural abundance among the elements in crustal rocks. Caesium melts at about 28° C (about 82° F), boils at about 669° C (about 1236° F), and has a relative density of 1.88; its atomic weight is 132.91. The natural source yielding the greatest quantity of caesium is the rare mineral pollux (or pollucite). Ores of this mineral found on the island of Elba contain 34 per cent of caesium oxide; American ores of pollux, found in Maine and South Dakota, contain 13 per cent of the oxide. Caesium ... occurs in lepidolite, carnallite, and certain feldspars. It is extracted by separating the caesium compound from the mineral, transforming the compound thus obtained into the cyanide, and electrolysis of the fused cyanide.
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Caesium was detected in 1860 by Robert Bunsen and Gustav Robert Kirchhoff. The two German scientists were analysing a sample of mineral water from Dürkheim, in Germany. They used a spectroscope on the sample and recognised the spectra from lithium, sodium and potassium. However, there were two vivid blue lines that did not correspond to any known element at that time. Bunsen and Kirchhoff concluded that they had identified a new element that they named caesium because of its emission spectrum. Twenty years after caesium had been identified, Carl Setterberg obtained a sample of the metal by electrolysis.
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