In quantities of more than about 100 grams (3.5 oz), caesium is shipped in hermetically sealed, stainless steel containers. Caesium can be stored in vacuum-sealed borosilicate glass ampoules. This is because caesium explodes instantly upon contact with water, leaving little time for hydrogen to accumulate. However, a caesium-water explosion is often less powerful than a sodium-water explosion with a similar amount of sodium. Similarly, it must be handled under inert gas, such as argon. It is stored and shipped in dry saturated hydrocarbons, such as mineral oil. Because of its high reactivity, the metal is classified as a hazardous material. The reaction with solid water occurs at temperatures as low as −116 ☌ (−177 ☏). In addition to igniting spontaneously in air, it reacts explosively with water even at low temperatures, more so than other members of the first group of the periodic table. Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk if released into the environment.Īddition of a small amount of caesium to cold water is explosive.Ĭaesium metal is highly reactive and very pyrophoric. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. It has a range of applications in the production of electricity, in electronics, and in chemistry. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. Since then, caesium has been widely used in highly accurate atomic clocks. In 1967, based on Einstein defining the speed of light as the most constant dimension in the universe, the International System of Units isolated two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the meter. 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. The metal is extremely reactive and pyrophoric, reacting with water even at −116 ☌ (−177 ☏). 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 ☌ (82 ☏), 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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