In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen to be used in the definition of the second by the International System of Units. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors. It is the least electronegative element having a stable isotope, caesium-133. The metal is extremely reactive and pyrophoric, reacting with water even at −116 ☌. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. It is a soft, silvery-gold alkali metal with a melting point of 28 ☌, which makes it one of only five elemental metals that are liquid at or near room temperature. 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.įreebase Rate this definition: 0.0 / 0 votesĬaesium or cesium is a chemical element with symbol Cs and atomic number 55. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. 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. Since then, caesium has been widely used in highly accurate atomic clocks. 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. The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. The element has 40 known isotopes, making it, along with barium and mercury, one of the elements with the most isotopes. It has only one stable isotope, caesium-133. It is the least electronegative element, with a value of 0.79 on the Pauling scale. It is pyrophoric and reacts with water even at −116 ☌ (−177 ☏). Caesium has physical and chemical properties similar to those of rubidium and potassium. It is a soft, silvery-golden alkali metal with a melting point of 28.5 ☌ (83.3 ☏), which makes it one of only five elemental metals that are liquid at or near room temperature. Wikipedia Rate this definition: 0.0 / 0 votesĬaesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55.
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