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Author: langbot
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English[en]
Caesium (IUPAC spelling[6]) (or cesium in American English)[note 1] is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F), which makes it one of only five elemental metals that are liquid at or near room temperature.[note 2] Caesium has physical and chemical properties similar to those of rubidium and potassium. The most reactive of all metals, it is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors. The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. In 1967, acting on Einstein's proof that the speed of light is the most constant dimension in the universe, the International System of Units used two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the metre. Since then, caesium has been widely used in highly accurate atomic clocks. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and ecological hazard in the environment.
Cornish[kw]
lven gymyk yw cesiom, niver 55 y'n Vosen Beriodek. Y furvell gymyk yw Cs. An hanow a dheu dhyworth an ger Latin caesius, ow styrya glaswynn, drefen liw y flamm. Nyns yw cesiom dhe les an korf denel. Diskudhys veu cesiom yn 1860 yn Heidelberg yn Almayn. Gwrys veu an ober gans Robert Bunsen (1811-1899), a dhevisas an losker Bunsen, ha Gustav Kirchoff (1824-1887), gans bryjyon 30,000 liter a dhowr moon. Askorrys yw 20 tunnas a cesiom yn unnik pub bledhen, gan an moyha rann ow tos dhyworth Kanada. Usys yw avel katalydh, dhe wul gweder optykal, ha dhe wul klockow atomek. Droglammow nuklerek hag arvow nuklerek re livras isotopow radyoweythresek dhe'n ayrgylgh. An cesiom-137 livrys gan an droglamm Chernobyl eth dres [Europa]] West oll, owth effeythi bargennyow tir deves yn Alban ha Kembra. Poos atomek cesiom yw 132.91 ha'y boynt teudhi yw 28°C ha'y boynt bryjyon yw 679°C. Y dhosedh yw 1.9kg an liter. Alkan medhel, golow, liw owr yw. Cesiom a dhasober gans dowr yn fest garow. Usys yw 'herdhyoryon' (thrusters) cesiom dhe lywya lorellow.