Caesium

Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at (or near) room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at −116 °C (−177 °F). It is the least electronegative element having a 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.

Two German chemists, Robert Bunsen and 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, 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. Since then, caesium has been widely used in atomic clocks.

Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. 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. Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk in case of radiation leaks.

Read more about Caesium:  Production, History, Health and Safety Hazards

Other articles related to "caesium":

Caesium Nitrate
... Caesium nitrate is a chemical compound with the chemical formula CsNO3 ... The caesium emissions are chiefly due to two powerful spectral lines at 852.113 nm and 894.347 nm ... Caesium nitrate prisms are used in infrared spectroscopy, in x-ray phosphors, and in scintillation counters ...
Caesium Oxide - Uses
... Caesium oxide is used in photocathodes to detect infrared signals in devices such as image intensifiers, vacuum photodiodes, photomultipliers, and TV camera ... described the first modern photoemissive surface in 1929–30 as a layer of caesium on a layer of caesium oxide on a layer of silver ...
Caesium Chloride - Physical Properties
... Caesium chloride is colorless in the form of large crystals and white when powdered ... Caesium chloride does not form hydrates. 72.96 In contrast to sodium chloride and potassium chloride, caesium chloride readily dissolves in concentrated hydrochloric acid ...
Time In Physics - Technology For Timekeeping Standards
... from the ammonia-based atomic clock (1949) to the caesium-based NBS-1 (1952) to NIST-7 (1993) ... time and frequency standard, a population of caesium atoms is laser-cooled to temperatures of one microkelvin ... The vertical lasers push the caesium ball through a microwave cavity ...
Caesium - Health and Safety Hazards
... Caesium compounds are rarely encountered by most people, but most are mildly toxic because of chemical similarity of caesium to potassium ... Exposure to large amounts of caesium compounds can cause hyperirritability and spasms, but as such amounts would not ordinarily be encountered in natural sources, caesium is not a major chemical environmental ... The median lethal dose (LD50) value for caesium chloride in mice is 2.3 g per kilogram, which is comparable to the LD50 values of potassium chloride and sodium chloride ...