Krypton

Main article: Isotopes of krypton
iso	NA	half-life	DM	DE (MeV)	DP
⁷⁸Kr	0.35%	2.3×10²⁰ y	ε ε	-	⁷⁸Se
⁷⁹Kr	syn	35.04 h	ε	-	⁷⁹Br
			β⁺	0.604	⁷⁹Br
			γ	0.26, 0.39, 0.60	-
⁸⁰Kr	2.25%	Kr is stable with 44 neutrons
⁸¹Kr	syn	2.29×10⁵ y	ε	-	⁸¹Br
⁸¹Kr	syn	2.29×10⁵ y	γ	0.281	-
⁸²Kr	11.6%	Kr is stable with 46 neutrons
⁸³Kr	11.5%	Kr is stable with 47 neutrons
⁸⁴Kr	57%	Kr is stable with 48 neutrons
⁸⁵Kr	syn	10.756 y	β^-	0.687	⁸⁵Rb
⁸⁶Kr	17.3%	Kr is stable with 50 neutrons

References

Krypton is a chemical element with the symbol Kr and atomic number 36. A colorless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionating liquefied air, and is often used with other rare gases in fluorescent lamps. Krypton is inert for most practical purposes but it is known to form compounds with fluorine. Krypton can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.

1 Notable characteristics
2 Applications
3 History
4 Occurrence
5 Compounds
6 Isotopes
7 Krypton fluoride laser
8 External links

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Notable characteristics

Krypton, a so-called noble gas due to its very low chemical reactivity, is characterized by a brilliant green and orange spectral signature. It is one of the products of uranium fission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure which is a common property of all "rare gases".

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Applications

The SI standard definition of the length of the metre was, from 1960 to 1983, based on the light emitted by excited krypton atoms: specifically, the metre 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.

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History

Krypton (Greek kryptos meaning "hidden") was discovered in 1898 by William Ramsay and Morris Travers in residue left from evaporating nearly all components of liquid air. In 1960 an international agreement defined the metre in terms of light emitted from a krypton isotope. This agreement replaced the longstanding standard metre 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 October 1983 the krypton standard was in turn replaced by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures). A metre is now defined as the distance that light travels in a vacuum during 1/299,792,458 s. The home planet of the popular comic book and movie hero "Superman", was named after this element. Superman's weakness "Kryptonite", was also named after this element.

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Occurrence

The concentration of this gas in earth's atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation.

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Compounds

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 oxy acid have also been found. ArKr+ and KrH+ molecule-ions have been investigated and there is evidence for KrXe or KrXe+.

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Isotopes

Naturally occurring krypton is made of five stable and one slightly radioactive 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 the fact that most Kr-85 is produced in the northern hemisphere, and north-south atmospheric mixing is relatively slow.

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Krypton fluoride laser

For more details on this topic, see Krypton fluoride laser.

One major use of krypton is the krypton fluoride laser. Certain amounts of energy are added to force krypton gas to react with fluorine gas to become krypton fluoride (KrF₂).

The compound will decompose once the energy supply stops. During the decomposition process, the excess chemical energy stored in the compound will be emitted in the form of strong laser energy.

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