![]() ![]() When in the presence of mineral oil (where it is best kept during transport), it loses its metallic lustre and takes on a duller, grey appearance. It is a very ductile, pale metal, which darkens in the presence of trace amounts of oxygen. ![]() Since then, caesium has been widely used in highly accurate atomic clocks.Ĭaesium is the softest element (it has a hardness of 0.2 Mohs). 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 first small-scale applications for caesium were as a " getter" in vacuum tubes and in photoelectric cells. The German chemist Robert Bunsen and physicist 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 has only one stable isotope, caesium-133. It is the least electronegative element, with a value of 0.79 on the Pauling scale. The most reactive of all metals, 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-gold 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. Although the element is only mildly toxic, the metal is a hazardous material and the radioisotopes present a significant health and ecological hazard in the environment.Ĭaesium 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. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. ![]() The most reactive of all metals, it is pyrophoric and reacts with water even at −116 ☌ (−177 ☏). It is a soft, silvery-gold 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. Caesium or cesium is a chemical element with symbol Cs and atomic number 55. ![]()
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