View source for Krypton

{{Short description|Chemical element with atomic number 36}}
{{about|the chemical element}}
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{{infobox krypton}}
'''Krypton''' (from {{langx|grc|κρυπτός|translit=kryptos}} 'the hidden one') is a [[chemical element]]; it has [[symbol (chemistry)|symbol]] '''Kr''' and [[atomic number]] 36. It is a colorless, odorless [[noble gas]] that occurs in [[trace element|trace amounts]] in the [[Earth's atmosphere|atmosphere]] and is often used with other rare gases in [[fluorescent lamp]]s. Krypton is [[chemically inert]].

Krypton, like the other noble gases, is used in lighting and [[photography]]. Krypton light has many [[spectral line]]s, and krypton [[Plasma (physics)|plasma]] is useful in bright, high-powered gas lasers (krypton [[ion laser|ion]] and [[excimer laser|excimer]] lasers), each of which resonates and amplifies a single spectral line. [[krypton fluoride laser|Krypton fluoride]] also makes a useful [[laser medium]]. From 1960 to 1983, the [[history of the metre#Krypton standard|official definition of the metre]] was based on the [[wavelength]] of one spectral line of krypton-86, because of the high power and relative ease of operation of krypton [[discharge tube]]s.

==History==
[[File:William Ramsay working.jpg|thumb|left|upright|Sir [[William Ramsay]], the discoverer of krypton]]
Krypton was discovered in [[Kingdom of Great Britain|Britain]] in 1898 by [[William Ramsay]], a Scottish chemist, and [[Morris Travers]], an English chemist, in residue left from evaporating nearly all components of [[liquid air]]. [[Neon]] was discovered by a similar procedure by the same workers just a few weeks later.<ref>{{cite journal
|title = On a New Constituent of Atmospheric Air
|author = William Ramsay
|author-link = William Ramsay
|author2 = Morris W. Travers
|journal = Proceedings of the Royal Society of London
|volume = 63
|issue = 1|pages = 405–408
|date = 1898|doi = 10.1098/rspl.1898.0051|doi-access = 
}}</ref> William Ramsay was awarded the 1904 [[Nobel Prize in Chemistry]] for discovery of a series of [[noble gas]]es, including krypton.<ref>{{Cite journal |last=Davies |first=Alwyn G. |date=March 2012 |title=Sir William Ramsay and the Noble Gases |journal=Science Progress |language=en |volume=95 |issue=1 |pages=23–49 |doi=10.3184/003685012X13307058213813 |pmid=22574384 |s2cid=12592582 |issn=0036-8504|pmc=10365523 }}</ref>

In 1960, the [[International Bureau of Weights and Measures]] defined the meter as 1,650,763.73 [[wavelength]]s of light emitted in the vacuum corresponding to the transition between the 2p<sub>10</sub> and 5d<sub>5</sub> levels in the [[isotope]] krypton-86.<ref>{{cite web|title=The BIPM and the evolution of the definition of the metre|url=http://www.bipm.org/en/measurement-units/history-si/evolution-metre.html|publisher=Bureau International des Poids et Mesures|date=2014-07-26|access-date=2016-06-23}}</ref><ref>{{cite web|title=Time Line for the Definition of the Meter|url=https://www.nist.gov/pml/div683/museum-timeline.cfm|first=William B.|last=Penzes|date=2009-01-08|access-date=2016-06-23|publisher=National Institute of Standards and Technology|archive-date=2016-08-12|archive-url=https://web.archive.org/web/20160812132330/http://nist.gov/pml/div683/museum-timeline.cfm|url-status=dead}}</ref> This agreement replaced the 1889 [[international prototype meter]], which was a metal bar located in [[Sèvres]]. This also made obsolete the 1927 definition of the [[ångström]] based on the red [[cadmium]] spectral line,<ref>{{cite journal |title=On the new determination of the meter |journal=Measurement Techniques |volume=1 |issue=3 |date=1958 |doi=10.1007/BF00974680 |pages=259–264 |first=G. D. |last=Burdun |bibcode=1958MeasT...1..259B |s2cid=121450003 }}</ref> replacing it with 1&nbsp;Å = 10<sup>−10</sup>&nbsp;m. The krypton-86 definition lasted until the October 1983 conference, which redefined the meter as the distance that light travels in [[vacuum]]<!--CORRECT FORMAL USAGE OMITS THE ARTICLE--> during 1/299,792,458&nbsp;s.<ref>{{cite book |url=https://books.google.com/books?id=ckyqWMwJXJMC&pg=PA122 |page=122 |title=The uncertainty of measurements: physical and chemical metrology: impact and analysis |author=Kimothi, Shri Krishna |publisher=American Society for Quality |date= 2002 |isbn=978-0-87389-535-4}}</ref><ref>{{cite web|url=http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html |title=How is the speed of light measured? |access-date=2007-03-19 |last=Gibbs |first=Philip |date=1997 |publisher=Department of Mathematics, University of California |url-status=dead |archive-url=https://web.archive.org/web/20150821181850/http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html |archive-date=2015-08-21 }}</ref><ref>[http://physics.nist.gov/cuu/Units/meter.html Unit of length (meter)], NIST</ref>

==Characteristics==
Krypton is characterized by several sharp emission lines ([[spectral signature]]s) the strongest being green and yellow.<ref name="colours">{{Cite web|url=http://astro.u-strasbg.fr/~koppen/discharge/|title=Spectra of Gas Discharges|access-date=2009-10-04|archive-url=https://web.archive.org/web/20110402185552/http://astro.u-strasbg.fr/%7Ekoppen/discharge/|archive-date=2011-04-02|url-status=dead}}</ref> Krypton is one of the products of [[uranium]] [[nuclear fission|fission]].<ref name="ANL">{{cite web|url=http://www.ead.anl.gov/pub/doc/krypton.pdf |archive-url=https://web.archive.org/web/20090929023106/http://www.ead.anl.gov/pub/doc/krypton.pdf |archive-date=2009-09-29 |title=Krypton |access-date=2007-03-17 |date=2005 |publisher=Argonne National Laboratory, EVS |url-status=dead }}</ref> Solid krypton is white and has a face-centered [[Cubic (crystal system)|cubic]] [[crystal structure]], which is a common property of all noble gases (except [[helium]], which has a hexagonal close-packed crystal structure).<ref>{{Cite journal |last1=Borden |first1=Brett |last2=Radin |first2=Charles |date=1981-08-15 |title=The crystal structure of the noble gases |url=https://aip.scitation.org/doi/abs/10.1063/1.442240 |journal=The Journal of Chemical Physics |volume=75 |issue=4 |pages=2012–2013 |doi=10.1063/1.442240 |bibcode=1981JChPh..75.2012B |issn=0021-9606}}</ref>

===Isotopes===
{{main|Isotopes of krypton}}
Naturally occurring krypton in Earth's atmosphere is composed of five [[Stable nuclide|stable]] [[isotopes]], plus one isotope (<sup>78</sup>Kr) with such a long [[half-life]] (9.2×10<sup>21</sup>&nbsp;years) that it can be considered stable. (This isotope has the third-longest known half-life among all isotopes for which decay has been observed; it undergoes [[double electron capture]] to <sup>78</sup>[[selenium|Se]]).<ref name="Patrignani2016" /><ref>{{cite journal |last1=Gavrilyuk |first1=Yu. M. |last2=Gangapshev |first2=A. M. |last3=Kazalov |first3=V. V. |last4=Kuzminov |first4=V. V. |last5=Panasenko |first5=S. I. |last6=Ratkevich |first6=S. S. |date=4 March 2013 |title=Indications of 2ν2K capture in <sup>78</sup>Kr |journal=Phys. Rev. C |volume=87 |issue=3 |pages=035501 |doi=10.1103/PhysRevC.87.035501|bibcode=2013PhRvC..87c5501G }}</ref> In addition, about thirty unstable isotopes and [[Nuclear isomer|isomers]] are known.<ref>{{RubberBible86th}}</ref> Traces of <sup>81</sup>Kr, a [[cosmogenic nuclide]] produced by the [[cosmic ray]] irradiation of <sup>80</sup>Kr, also occur in nature: this [[isotope]] is [[radioactive]] with a half-life of 230,000 years. Krypton is highly volatile and does not stay in solution in near-surface water, but <sup>81</sup>Kr has been used for [[radiometric dating|dating]] old (50,000–800,000 years) [[groundwater]].<ref>{{cite web |url=https://digital.library.unt.edu/ark:/67531/metadc737461/m2/1/high_res_d/809813.pdf |title=Development of Laser-Based Resonance Ionization Techniques for 81-Kr and 85-Kr Measurements in the Geosciences |access-date=2007-03-20 |last1=Thonnard |first1=Norbert |last2=MeKay |first2=Larry D. |last3=Labotka |first3=Theodore C. |date=2001-02-05 |publisher=University of Tennessee, Institute for Rare Isotope Measurements |pages=4–7}}</ref>

[[Krypton-85|<sup>85</sup>Kr]] is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the [[nuclear fission|fission]] of [[uranium]] and [[plutonium]], such as in [[nuclear bomb]] testing and [[nuclear reactor]]s. <sup>85</sup>Kr is released during the reprocessing of [[fuel rod]]s from nuclear reactors. Concentrations at the [[North Pole]] are 30% higher than at the [[South Pole]] due to convective mixing.<ref>{{cite web |url=http://wwwrcamnl.wr.usgs.gov/isoig/period/kr_iig.html |archive-url=https://web.archive.org/web/20010924204348/http://wwwrcamnl.wr.usgs.gov/isoig/period/kr_iig.html |url-status=dead |archive-date=2001-09-24 |title=Resources on Isotopes |access-date=2007-03-20 |publisher=U.S. Geological Survey }}</ref>

===Chemistry===
Like the other noble gases, krypton is chemically highly unreactive. The rather restricted chemistry of krypton in the +2 oxidation state parallels that of the neighboring element [[bromine]] in the +1 oxidation state; due to the [[scandide contraction]] it is difficult to oxidize the 4p elements to their group oxidation states. Until the 1960s no noble gas compounds had been synthesized.<ref name="S&E">{{cite web |url=http://pubs.acs.org/cen/80th/noblegases.html|title=The Noble Gases|access-date=2006-07-02 |last=Bartlett |first=Neil |date=2003|publisher=Chemical & Engineering News}}</ref>

Following the first successful synthesis of [[xenon]] compounds in 1962, synthesis of [[krypton difluoride]] ({{chem|KrF|2}}) was reported in 1963. In the same year, {{chem|KrF|4}} was reported by Grosse, ''et al.'',<ref>{{Cite journal | doi = 10.1126/science.139.3559.1047 | title = Krypton Tetrafluoride: Preparation and Some Properties | year = 1963 | last1 = Grosse | first1 = A. V. | last2 = Kirshenbaum | first2 = A. D. | last3 = Streng | first3 = A. G. | last4 = Streng | first4 = L. V. | journal = Science | volume = 139| issue = 3559 | pages = 1047–1048| pmid = 17812982 |bibcode = 1963Sci...139.1047G }}</ref> but was subsequently shown to be a mistaken identification.<ref>{{Cite journal | doi = 10.1007/BF01375764 | title = Krypton difluoride | year = 1971 | last1 = Prusakov | first1 = V. N. | last2 = Sokolov | first2 = V. B. | journal = Soviet Atomic Energy | volume = 31 | issue = 3| pages = 990–999 | s2cid = 189775335 }}</ref> Under extreme conditions, krypton reacts with fluorine to form KrF<sub>2</sub> according to the following equation:

:<chem>Kr + F2 -> KrF2</chem>

Krypton gas in a [[krypton fluoride laser]] absorbs energy from a source, causing the krypton to react with fluorine gas, producing the exciplex krypton fluoride, a temporary [[complex (chemistry)|complex]] in an excited energy state:<ref>{{Cite journal |last1=Johnson |first1=Thomas H. |last2=Hunter |first2=Allen M. |date=1980-05-01 |title=Physics of the krypton fluoride laser |journal=Journal of Applied Physics |volume=51 |issue=5 |pages=2406–2420 |doi=10.1063/1.328010 |bibcode=1980JAP....51.2406J |issn=0021-8979|doi-access=free }}</ref>

:<chem>2Kr + F2 -> 2KrF</chem>

The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly [[repulsive state|repulsive ground state]]. The ground state complex quickly dissociates into unbound atoms:

:<chem>2KrF -> 2Kr + F2</chem>

The result is an [[excimer laser|exciplex laser]] which radiates energy at 248&nbsp;nm, near the [[ultraviolet]] portion of the [[spectrum]], corresponding with the energy difference between the ground state and the excited state of the complex.<ref>{{Cite journal |last1=Preston |first1=S. G. |last2=Sanpera |first2=A. |last3=Zepf |first3=M. |last4=Blyth |first4=W. J. |last5=Smith |first5=C. G. |last6=Wark |first6=J. S. |last7=Key |first7=M. H. |last8=Burnett |first8=K. |last9=Nakai |first9=M. |last10=Neely |first10=D. |last11=Offenberger |first11=A. A. |date=1996-01-01 |title=High-order harmonics of 248.6-nm KrF laser from helium and neon ions |url=https://link.aps.org/doi/10.1103/PhysRevA.53.R31 |journal=Physical Review A |volume=53 |issue=1 |pages=R31–R34 |doi=10.1103/PhysRevA.53.R31|pmid=9912935 |bibcode=1996PhRvA..53...31P }}</ref>

[[File:Krypton hydride crystal.jpg|thumb|left|Kr(H<sub>2</sub>)<sub>4</sub> and H<sub>2</sub> solids formed in a [[diamond anvil cell]]<ref name="KrH" />]]
[[File:Krypton hydride structure.png|thumb|Structure of Kr(H<sub>2</sub>)<sub>4</sub>. Krypton octahedra (green) are surrounded by randomly oriented hydrogen molecules.<ref name="KrH" />]]
Compounds with krypton bonded to atoms other than [[fluorine]] have also been discovered. There are also unverified reports of a [[barium]] [[Salt (chemistry)|salt]] of a krypton [[oxoacid]].<ref>{{Cite journal| doi = 10.1126/science.143.3603.242| pmid = 17753149| year = 1964| last1 = Streng | first1 = A.| last2 = Grosse | first2 = A.| title = Acid of Krypton and Its Barium Salt| volume = 143| issue = 3603| pages = 242–243| journal = Science |bibcode = 1964Sci...143..242S | s2cid = 11607538}}</ref> [[argon|Ar]]Kr<sup>+</sup> and Kr[[hydrogen|H]]<sup>+</sup> [[polyatomic ions]] have been investigated and there is evidence for Kr[[xenon|Xe]] or KrXe<sup>+</sup>.<ref>{{cite web |url=http://www.bu.edu/ehs/ih/pdf/periodic_table.pdf |title=Periodic Table of the Elements|access-date=2007-04-05 |publisher=Los Alamos National Laboratory's Chemistry Division |pages=100–101 |archive-url =https://web.archive.org/web/20061125134307/http://www.bu.edu/ehs/ih/pdf/periodic_table.pdf |archive-date = November 25, 2006}}</ref>

The reaction of {{chem|KrF|2}} with {{chem|B(OTeF|5|)|3}} produces an unstable compound, {{chem|Kr(OTeF|5|)|2}}, that contains a krypton-[[oxygen]] bond. A krypton-[[nitrogen]] bond is found in the [[cation]] [HC≡N–Kr–F]{{su|p=+}}, produced by the reaction of {{chem|KrF|2}} with [HC≡NH]{{su|p=+}}[AsF{{su|b=6|p=−}}] below −50&nbsp;°C.<ref>{{cite book| title = Advances in Inorganic Chemistry| url = https://archive.org/details/isbn_0120236451| url-access = limited|author = Holloway, John H. |author2 = Hope, Eric G. |editor = Sykes, A. G. | publisher = Academic Press|date = 1998| isbn = 978-0-12-023646-6|page = [https://archive.org/details/isbn_0120236451/page/n59 57]}}</ref><ref>{{cite book
| title = Modeling Marvels: Computational Anticipation of Novel Molecules
| author = Lewars, Errol G.
| publisher = Springer
| date = 2008
| isbn = 978-1-4020-6972-7
| page = 68
| url = https://books.google.com/books?id=whdw2qlXjD0C}}</ref> HKrCN and HKrC≡CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 [[kelvin|K]].<ref name="S&E" />

Krypton [[hydride]] (Kr(H<sub>2</sub>)<sub>4</sub>) crystals can be grown at pressures above 5&nbsp;GPa. They have a face-centered cubic structure where krypton octahedra are surrounded by randomly oriented hydrogen molecules.<ref name="KrH">{{cite journal|doi=10.1038/srep04989|title=New high-pressure van der Waals compound Kr(H<sub>2</sub>)<sub>4</sub> discovered in the krypton-hydrogen binary system|journal=Scientific Reports|volume=4|pages=4989|year=2014|last1=Kleppe|first1=Annette K.|last2=Amboage|first2=Mónica|last3=Jephcoat|first3=Andrew P.|bibcode=2014NatSR...4.4989K|doi-access=free}}</ref>

===Natural occurrence===
Earth has retained all of the noble gases that were present at its formation except [[helium]]. Krypton's concentration in the [[Earth's atmosphere|atmosphere]] is about 1&nbsp;[[part per million|ppm]]. It can be extracted from liquid air by [[fractional distillation]].<ref>{{cite web |url=http://www.madehow.com/Volume-4/Krypton.html|title=How Products are Made: Krypton|access-date=2006-07-02}}</ref> The amount of krypton in space is uncertain, because measurement is derived from meteoric activity and solar winds. The first measurements suggest an abundance of krypton in space.<ref>{{Cite journal|last=Cardelli|first=Jason A.|author2=Meyer, David M.|year=1996|title=The Abundance of Interstellar Krypton|journal=The Astrophysical Journal Letters|volume=477|issue=1|pages=L57–L60|bibcode=1997ApJ...477L..57C|doi=10.1086/310513|doi-access=free}}<!--|access-date=2007-04-05 --></ref>

==Applications==
[[File:KrTube.jpg|left|thumb|Krypton gas discharge tube]]
Krypton's multiple emission lines make ionized krypton gas discharges appear whitish, which in turn makes krypton-based bulbs useful in photography as a white light source. Krypton is used in some photographic flashes for high speed [[photography]]. Krypton gas is also combined with mercury to make luminous signs that glow with a bright greenish-blue light.<ref>{{cite web |url=http://www.capecodextension.org/pdfs/Mercury%20Lighting.pdf |archive-url=https://web.archive.org/web/20070929085332/http://www.capecodextension.org/pdfs/Mercury%20Lighting.pdf |url-status=dead |archive-date=2007-09-29 |title=Mercury in Lighting |access-date=2007-03-20 |publisher=Cape Cod Cooperative Extension }}</ref>

Krypton is mixed with [[argon]] in energy efficient fluorescent lamps, reducing the power consumption, but also reducing the light output and raising the cost.<ref>[https://web.archive.org/web/20100912181537/http://www.anaheim.net/utilities/ea/PA_11.html Lighting: Full-Size Fluorescent Lamps]. McGraw-Hill Companies, Inc. (2002)</ref> Krypton costs about 100 times as much as argon. Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higher [[operating temperature]]s.<ref>[http://www.uigi.com/rare_gases.html Properties, Applications and Uses of the "Rare Gases" Neon, Krypton and Xenon]. Uigi.com. Retrieved on 2015-11-30.</ref>

Krypton's white discharge is sometimes used as an artistic effect in gas discharge "neon" tubes. Krypton produces much higher light power than neon in the red spectral line region, and for this reason, red lasers for high-power laser light-shows are often krypton lasers with mirrors that select the red spectral line for laser amplification and emission, rather than the more familiar helium-neon variety, which could not achieve the same multi-watt outputs.<ref>{{cite web|url=http://www.gameops.com/content/pdf/laser_terms.pdf|title=Laser Devices, Laser Shows and Effect|access-date=2007-04-05|archive-url=https://web.archive.org/web/20070221093633/http://www.gameops.com/content/pdf/laser_terms.pdf|archive-date=2007-02-21|url-status=dead}}</ref>

The [[krypton fluoride laser]] is important in nuclear fusion energy research in confinement experiments. The [[laser]] has high beam uniformity, short [[wavelength]], and the spot size can be varied to track an imploding pellet.<ref>{{cite web |url=http://aries.ucsd.edu/LIB/MEETINGS/IAEAIFECRP/PDF/Sethian.pdf |title=Krypton Fluoride Laser Development for Inertial Fusion Energy |access-date=2007-03-20 |last=Sethian |first=J. |author2=M. Friedman |author3=M. Myers |publisher=Plasma Physics Division, Naval Research Laboratory |pages=1–8 |archive-date=2011-09-29 |archive-url=https://web.archive.org/web/20110929041103/http://aries.ucsd.edu/LIB/MEETINGS/IAEAIFECRP/PDF/Sethian.pdf |url-status=dead }}</ref>

In experimental [[particle physics]], liquid krypton is used to construct quasi-homogeneous electromagnetic [[Calorimeter (particle physics)|calorimeters]]. A notable example is the calorimeter of the [[NA48]] experiment at [[CERN]] containing about 27 [[tonne]]s of liquid krypton. This usage is rare, since liquid [[argon]] is less expensive. The advantage of krypton is a smaller [[Molière radius]] of 4.7&nbsp;cm, which provides excellent spatial resolution with little overlapping. The other parameters relevant for calorimetry are: [[radiation length]] of X<sub>0</sub>=4.7&nbsp;cm, and density of 2.4&nbsp;g/cm<sup>3</sup>.

Krypton-83 has application in [[magnetic resonance imaging]] (MRI) for imaging airways. In particular, it enables the radiologist to distinguish between [[Hydrophobe|hydrophobic]] and hydrophilic surfaces containing an airway.<ref name="Pavlovskaya">{{cite journal |display-authors=4 |author=Pavlovskaya, GE |author2=Cleveland, ZI |author3=Stupic, KF |author4=Basaraba, RJ |author5=Meersmann, T |title=Hyperpolarized krypton-83 as a contrast agent for magnetic resonance imaging |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=102 |issue=51 |pages=18275–9 |date=2005|pmid=16344474 |pmc=1317982 |doi=10.1073/pnas.0509419102|bibcode = 2005PNAS..10218275P |doi-access=free }}</ref>

Although xenon has potential for use in [[computed tomography]] (CT) to assess regional ventilation, its anesthetic properties limit its fraction in the breathing gas to 35%. A breathing mixture of 30% xenon and 30% krypton is comparable in effectiveness for CT to a 40% xenon fraction, while avoiding the unwanted effects of a high partial pressure of xenon gas.<ref>{{cite journal |display-authors=4 |author=Chon, D |author2=Beck, KC |author3=Simon, BA |author4=Shikata, H |author5=Saba, OI |author6=Hoffman, EA |title=Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements |journal=Journal of Applied Physiology |volume=102 |issue=4 |pages=1535–44 |date=2007 |pmid=17122371 |doi=10.1152/japplphysiol.01235.2005}}</ref> The [[metastable isotope]] krypton-81m is used in [[nuclear medicine]] for lung [[ventilation/perfusion scan]]s, where it is inhaled and imaged with a [[gamma camera]].<ref>{{cite journal|last1=Bajc|first1=M.|last2=Neilly|first2=J. B.|last3=Miniati|first3=M.|last4=Schuemichen|first4=C.|last5=Meignan|first5=M.|last6=Jonson|first6=B.|title=EANM guidelines for ventilation/perfusion scintigraphy|journal=European Journal of Nuclear Medicine and Molecular Imaging|date=27 June 2009|volume=36|issue=8|pages=1356–1370|doi=10.1007/s00259-009-1170-5|pmid=19562336|doi-access=free|hdl=2158/774307|hdl-access=free}}</ref> Krypton-85 in the atmosphere has been used to detect clandestine nuclear fuel reprocessing facilities in [[North Korea]]<ref>{{Cite news|url = http://www.highbeam.com/doc/1P2-6961236.html|archive-url = https://web.archive.org/web/20160409224307/https://www.highbeam.com/doc/1P2-6961236.html|url-status = dead|archive-date = 2016-04-09|title = N. Korea may be hiding new nuclear site|last1 = Sanger|first1 = David E.|date = 2003-07-20|work = Oakland Tribune|access-date = 2015-05-01|first2 = Thom|last2 = Shanker}}</ref> and [[Pakistan]].<ref>{{Cite news|url = http://www.highbeam.com/doc/1P1-29474075.html|archive-url = https://web.archive.org/web/20161018215155/https://www.highbeam.com/doc/1P1-29474075.html|url-status = dead|archive-date = 2016-10-18|title = U.S. Intelligence Find Evidence of Pakistan Producing Nuclear Weapons, CBS|last1 = Bradley|first1 = Ed|date = 2000-03-16|work = CBS Evening News with Dan Rather|access-date = 2015-05-01|first2 = David|last2 = Martin}}</ref> Those facilities were detected in the early 2000s and were believed to be producing weapons-grade plutonium. Krypton-85 is a medium lived [[fission product]] and thus escapes from [[spent fuel]] when the cladding is removed.<ref>{{Cite journal |last=Różański |first=K. |date=1979-01-01 |title=Krypton-85 in the atmosphere 1950–1977: a data review |url=https://dx.doi.org/10.1016/0160-4120%2879%2990071-0 |journal=Environment International |language=en |volume=2 |issue=3 |pages=139–143 |doi=10.1016/0160-4120(79)90071-0 |bibcode=1979EnInt...2..139R |issn=0160-4120}}</ref>

Krypton is used occasionally as an insulating gas between window panes.<ref>{{cite web|last1=Ayre|first1=James|title=Insulated Windows 101 — Double Glazing, Triple Glazing, Thermal Performance, & Potential Problems|url=https://cleantechnica.com/2018/04/28/insulated-windows-101-double-glazing-triple-glazing-thermal-performance-potential-problems/|website=[[cleantechnica.com]]|access-date=17 May 2018|date=2018-04-28}}</ref> [[SpaceX]] [[Starlink]] uses krypton as a propellant for their [[hall-effect thruster|electric propulsion system]].<ref>{{Cite web|url=https://www.youtube.com/watch?v=riBaVeDTEWI&t=430| archive-url=https://ghostarchive.org/varchive/youtube/20211103/riBaVeDTEWI| archive-date=2021-11-03 | url-status=live|title=Starlink Mission|last=SpaceX| website=[[YouTube]]| date=23 May 2019|time=7:10}}{{cbignore}}</ref>

==Precautions==
[[File:The Meyer-Overton correlation.png|thumb|upright=1.1|class=skin-invert-image|Krypton compared to other anaesthetic gases (minimum alveolar concentration is an inverse indicator of potency)]]
Krypton is considered to be a non-toxic [[asphyxiant gas|asphyxiant]].<ref>[http://pt.chemicalstore.com/Kr%20-%20Krypton.html Properties of Krypton] {{webarchive|url=https://web.archive.org/web/20090219024551/http://pt.chemicalstore.com/Kr%20-%20Krypton.html |date=2009-02-19 }}. Pt.chemicalstore.com. Retrieved on 2015-11-30.</ref> Being [[lipophilic]], krypton has a significant anaesthetic effect (although the mechanism of this phenomenon is still [[Theories of general anaesthetic action|not fully clear]],<ref>{{Cite journal |last1=Kennedy |first1=R. R. |last2=Stokes |first2=J. W. |last3=Downing |first3=P. |date=February 1992 |title=Anaesthesia and the 'Inert' Gases with Special Reference to Xenon |journal=Anaesthesia and Intensive Care |language=en |volume=20 |issue=1 |pages=66–70 |doi=10.1177/0310057X9202000113 |pmid=1319119 |s2cid=29886337 |issn=0310-057X|doi-access=free }}</ref> there is good evidence that the two properties are mechanistically related), with [[Nitrogen narcosis#Causes|narcotic potency]] seven times greater than air, and breathing an atmosphere of 50% krypton and 50% natural air (as might happen in the locality of a leak) causes [[Narcosis (disambiguation)|narcosis]] in humans similar to breathing air at four times atmospheric pressure. This is comparable to scuba diving at a depth of {{convert|30|m|ft|abbr=on|sigfig=1}} and could affect anyone breathing it.

==In popular culture==
[[DC Comics]] superhero [[Superman|Superman's]] home planet is named [[Krypton (comics)|Krypton]]. The planet was created by [[Jerry Siegel]] and [[Joe Shuster]] and was named after the chemical element. The planet was first mentioned in ''[[Action Comics]]'' #1 (June 1938) and made its first appearance in [[Superman (comic book)|''Superman'']] #1 (1939).

{{Subject bar
|book1=Krypton
|book2=Period 4 elements
|book3=Noble gases
|book4=Chemical elements (sorted&nbsp;alphabetically)
|book5=Chemical elements (sorted by number)
|portal=Chemistry
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|wikt=y
|wikt-search=krypton
|v=y
|v-search=Krypton atom
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==References==
{{Reflist|colwidth=30em}}

==Further reading==
* William P. Kirk [http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9100FW8L.txt "Krypton 85: a Review of the Literature and an Analysis of Radiation Hazards"], Environmental Protection Agency, Office of Research and Monitoring, Washington (1972)

==External links==
* [http://www.periodicvideos.com/videos/036.htm Krypton] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://web.archive.org/web/20070203205901/http://other.nrl.navy.mil/LaserFusionEnergy/lasercreation.htm Krypton Fluoride Lasers], Plasma Physics Division Naval Research Laboratory
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[[Category:Krypton| ]]
[[Category:Chemical elements]]
[[Category:Noble gases]]