Krypton is a so-called noble gas due to its very low chemical reactivity and it is characterized by a brilliant green and orangespectral signature[?]. It is one of the products of uraniumfission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure which is a common property of all "rare gases."
The international definition of the length of the meter was, from 1960 to 1983, based on the light emitted by excited krypton atoms as a standard: specifically, the meter was defined as 1,650,763.73 wavelengths of the orange-red emission line emitted by krypton-86 atoms.
Krypton clathrates[?] have been made with hydroquinone and phenol. Kr-85 is used in chemical analysis. When it is placed in various solids kryptonates[?] are formed and their activity is sensitive to surface chemical reactions. This noble gas is also used in photographic flash lamps needed for high-speed photography but this use is limited because of the high cost of krypton.
Krypton (Greekkryptos meaning "hidden") was discovered in 1898 by William Ramsay and Morris Travers[?] in residue from evaporating nearly components of liquid air. In 1960 an international agreement defined the meter in terms of light emitted from a krypton isotope. This agreement replaced the longstanding standard meter[?] located in Paris which was a metal bar made of a platinum-iridium alloy (the bar was originally estimated to be one ten millionth of a quadrant of the earth's polar circumference). In October1983 the krypton standard was in turn replaced by the International Bureau of Weights and Measures. A meter is now defined as the distance that light traveles in a vacuum during 1/299,792,458 s.
Like the other rare gases krypton is widely considered to be chemically inert. However, studies conducted since the 1960s have uncovered some compounds of krypton. Krypton difluoride has been made in gram quantities and can be produced in several different ways. Other fluorides and a salt of a krypton called oxyacid have also been found. ArKr+ and KrH+ molecule-ions have been investigated and there is evidence for KrXe or KrXe+.
Naturally occurring krypton is composed of six stable isotopes. Krypton's spectral signature is easily produced with some very sharp lines. Kr-81 is the product of atmospheric reactions with the other naturally occurring isotopes of krypton. It is radioactive with a half-life of 250,000 years. Like xenon, krypton is highly volatile when it is near surface waters and Kr-81 has therefore been used for dating old (50,000 - 800,000 year) groundwater[?].
Kr-85 is an inert radioactive noble gas with a half-life of 10.76 years, that is produced by fission of uranium and plutonium. Sources have included nuclear bomb testing, nuclear reactors, and the release of Kr-85 during the reprocessing of fuel rods[?] from nuclear reactors. A strong gradient exists between the northern and southern hemispheres where concentrations at the North Pole are approximately 30% higher than the South Pole due to convective mixing.
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