 = Xenon = 
 
 Xenon is a chemical element with symbol Xe and atomic number 54 . It is a colorless , dense , <unk> noble gas , that occurs in the Earth 's atmosphere in trace amounts . Although generally <unk> , xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate , the first noble gas compound to be synthesized . 
 Xenon is used in flash lamps and arc lamps , and as a general anesthetic . The first excimer laser design used a xenon dimer molecule ( <unk> ) as its <unk> medium , and the earliest laser designs used xenon flash lamps as pumps . Xenon is also being used to search for hypothetical weakly interacting massive particles and as the propellant for ion <unk> in spacecraft . 
 Naturally occurring xenon consists of eight stable isotopes . There are also over 40 unstable isotopes that undergo radioactive decay . The isotope ratios of xenon are an important tool for studying the early history of the Solar System . <unk> xenon @-@ 135 is produced by beta decay from iodine @-@ 135 ( which is a product of nuclear fission ) , and it acts as the most significant neutron <unk> in nuclear reactors . 
 
 = = History = = 
 
 Xenon was discovered in England by the Scottish chemist William Ramsay and English chemist Morris Travers in September 1898 , shortly after their discovery of the elements krypton and neon . They found xenon in the residue left over from <unk> components of liquid air . Ramsay suggested the name xenon for this gas from the Greek word <unk> [ xenon ] , <unk> singular form of <unk> [ <unk> ] , meaning ' foreign ( er ) ' , ' strange ( r ) ' , or ' guest ' . In 1902 , Ramsay estimated the proportion of xenon in the Earth 's atmosphere as one part in 20 million . 
 During the 1930s , American engineer Harold <unk> began exploring <unk> light technology for high speed photography . This led him to the invention of the xenon flash lamp , in which light is generated by sending a brief electric current through a tube filled with xenon gas . In 1934 , <unk> was able to generate flashes as brief as one <unk> with this method . 
 In 1939 , American physician Albert R. <unk> Jr. began exploring the causes of " <unk> " in deep @-@ sea divers . He tested the effects of varying the breathing mixtures on his subjects , and discovered that this caused the divers to perceive a change in depth . From his results , he deduced that xenon gas could serve as an anesthetic . Although Russian <unk> <unk> V. <unk> apparently studied xenon anesthesia in 1941 , the first published report confirming xenon anesthesia was in 1946 by American medical researcher John H. Lawrence , who experimented on mice . Xenon was first used as a surgical anesthetic in 1951 by American <unk> Stuart C. Cullen , who successfully operated on two patients . 
 Xenon and the other noble gases were for a long time considered to be completely chemically inert and not able to form compounds . However , while teaching at the University of British Columbia , Neil Bartlett discovered that the gas platinum hexafluoride ( PtF6 ) was a powerful oxidizing agent that could <unk> oxygen gas ( O2 ) to form <unk> hexafluoroplatinate ( O2 + [ PtF6 ] − ) . Since O2 and xenon have almost the same first ionization potential , Bartlett realized that platinum hexafluoride might also be able to <unk> xenon . On March 23 , 1962 , he mixed the two gases and produced the first known compound of a noble gas , xenon hexafluoroplatinate . Bartlett thought its composition to be Xe + [ PtF6 ] − , although later work has revealed that it was probably a mixture of various xenon @-@ containing salts . Since then , many other xenon compounds have been discovered , along with some compounds of the noble gases argon , krypton , and <unk> , including argon <unk> ( <unk> ) , krypton difluoride ( <unk> ) , and <unk> fluoride . By 1971 , more than 80 xenon compounds were known . 
 In November 1999 IBM scientists demonstrated a technology capable of manipulating individual atoms . The program , called IBM in atoms , used a scanning <unk> microscope to arrange 35 individual xenon atoms on a substrate of <unk> crystal of nickel to spell out the three letter company acronym . It was the first time atoms had been precisely positioned on a flat surface . 
 
 = = Characteristics = = 
 
 Xenon has atomic number 54 ; that is , its nucleus contains 54 protons . At standard temperature and pressure , pure xenon gas has a density of 5 @.@ 761 kg / m3 , about 4 @.@ 5 times the surface density of the Earth 's atmosphere , 1 @.@ 217 kg / m3 . As a liquid , xenon has a density of up to 3 @.@ 100 g / <unk> , with the density maximum occurring at the triple point . Notably , liquid xenon has a high <unk> due to its large atomic volume , and thus is an excellent solvent . It can dissolve <unk> , biological molecules , and even water . Under the same conditions , the density of solid xenon , 3 @.@ 640 g / cm3 , is higher than the average density of granite , 2 @.@ 75 g / cm3 . Using <unk> of pressure , xenon has been forced into a metallic phase . 
 Solid xenon changes from face @-@ centered cubic ( <unk> ) to <unk> close packed ( <unk> ) crystal phase under pressure and begins to turn metallic at about 140 GPa , with no noticeable volume change in the <unk> phase . It is completely metallic at 155 GPa . When <unk> , xenon looks sky blue because it absorbs red light and <unk> other visible frequencies . Such behavior is unusual for a metal and is explained by the relatively small widths of the electron bands in metallic xenon . 
 Liquid or solid xenon <unk> can be formed at room temperature by <unk> Xe + ions into a solid matrix . Many solids have lattice <unk> smaller than solid Xe . This results in compression of the implanted Xe to pressures that may be sufficient for its <unk> or <unk> . 
 Xenon is a member of the zero @-@ valence elements that are called noble or inert gases . It is inert to most common chemical reactions ( such as combustion , for example ) because the outer valence shell contains eight electrons . This produces a stable , minimum energy configuration in which the outer electrons are tightly bound . 
 In a gas @-@ filled tube , xenon emits a blue or <unk> glow when the gas is excited by electrical discharge . Xenon emits a band of emission lines that span the visual spectrum , but the most intense lines occur in the region of blue light , which produces the coloration . 
 
 = = Occurrence and production = = 
 
 Xenon is a trace gas in Earth 's atmosphere , occurring at 87 ± 1 parts per billion ( <unk> / L ) , or approximately 1 part per 11 @.@ 5 million , and is also found as a component in gases emitted from some mineral springs . 
 Xenon is obtained commercially as a by @-@ product of the separation of air into oxygen and nitrogen . After this separation , generally performed by <unk> distillation in a double @-@ column plant , the liquid oxygen produced will contain small quantities of krypton and xenon . By additional <unk> distillation steps , the liquid oxygen may be enriched to contain 0 @.@ 1 – 0 @.@ 2 % of a krypton / xenon mixture , which is extracted either via absorption onto <unk> gel or by distillation . Finally , the krypton / xenon mixture may be separated into krypton and xenon via distillation . Worldwide production of xenon in 1998 was estimated at 5 @,@ 000 – 7 @,@ 000 m3 . Because of its low abundance , xenon is much more expensive than the lighter noble gases — approximate prices for the purchase of small quantities in Europe in 1999 were 10 € / L for xenon , 1 € / L for krypton , and 0 @.@ 20 € / L for neon ; the much more plentiful argon costs less than a cent per <unk> . 
 Within the Solar System , the <unk> fraction of xenon is 1 @.@ 56 × 10 − 8 , for an abundance of approximately one part in 630 thousand of the total mass . Xenon is relatively rare in the Sun 's atmosphere , on Earth , and in asteroids and comets . The planet Jupiter has an unusually high abundance of xenon in its atmosphere ; about 2 @.@ 6 times as much as the Sun . This high abundance remains unexplained and may have been caused by an early and rapid buildup of <unk> — small , <unk> bodies — before the <unk> disk began to heat up . ( Otherwise , xenon would not have been trapped in the <unk> <unk> . ) The problem of the low terrestrial xenon may potentially be explained by <unk> bonding of xenon to oxygen within <unk> , hence reducing the outgassing of xenon into the atmosphere . 
 Unlike the lower mass noble gases , the normal stellar nucleosynthesis process inside a star does not form xenon . Elements more massive than iron @-@ 56 have a net energy cost to produce through fusion , so there is no energy gain for a star when creating xenon . Instead , xenon is formed during supernova explosions , by the slow neutron capture process ( s @-@ process ) of red giant stars that have exhausted the hydrogen at their cores and entered the asymptotic giant branch , in classical nova explosions and from the radioactive decay of elements such as iodine , uranium and plutonium . 
 
 = = Isotopes and isotopic studies = = 
 
 Naturally occurring xenon is made of eight stable isotopes , the most of any element with the exception of tin , which has ten . Xenon and tin are the only elements to have more than seven stable isotopes . The isotopes <unk> and <unk> are predicted to undergo double beta decay , but this has never been observed so they are considered to be stable . Besides these stable forms , there are over 40 unstable isotopes that have been studied . The longest lived of these isotopes is <unk> , which has been observed to undergo double beta decay with a half @-@ life of 2 @.@ 11 × <unk> <unk> . 129Xe is produced by beta decay of 129I , which has a half @-@ life of 16 million years , while <unk> , 133Xe , <unk> , and 135Xe are some of the fission products of both <unk> and <unk> , and therefore used as indicators of nuclear explosions . 
 <unk> of two of the stable isotopes of xenon , 129Xe and <unk> , have non @-@ zero intrinsic angular <unk> ( nuclear spins , suitable for nuclear magnetic resonance ) . The nuclear spins can be aligned beyond ordinary polarization levels by means of <unk> polarized light and <unk> vapor . The resulting spin polarization of xenon nuclei can surpass 50 % of its maximum possible value , greatly exceeding the thermal equilibrium value dictated by <unk> statistics ( typically 0 @.@ 001 % of the maximum value at room temperature , even in the strongest magnets ) . Such non @-@ equilibrium alignment of spins is a temporary condition , and is called <unk> . The process of <unk> the xenon is called optical pumping ( although the process is different from pumping a laser ) . 
 Because a 129Xe nucleus has a spin of 1 / 2 , and therefore a zero electric <unk> moment , the 129Xe nucleus does not experience any <unk> interactions during collisions with other atoms , and thus its <unk> can be maintained for long periods of time even after the laser beam has been turned off and the alkali vapor removed by condensation on a room @-@ temperature surface . Spin polarization of 129Xe can persist from several seconds for xenon atoms dissolved in blood to several hours in the gas phase and several days in deeply frozen solid xenon . In contrast , <unk> has a nuclear spin value of 3 ⁄ 2 and a <unk> <unk> moment , and has t1 relaxation times in the <unk> and second ranges . 
 Some radioactive isotopes of xenon , for example , 133Xe and 135Xe , are produced by neutron irradiation of <unk> material within nuclear reactors . 135Xe is of considerable significance in the operation of nuclear fission reactors . 135Xe has a huge cross section for thermal neutrons , 2 @.@ 6 × 106 <unk> , so it acts as a neutron <unk> or " poison " that can slow or stop the chain reaction after a period of operation . This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production . Fortunately the designers had made provisions in the design to increase the reactor 's reactivity ( the number of neutrons per fission that go on to fission other atoms of nuclear fuel ) . 135Xe reactor poisoning played a major role in the <unk> disaster . A <unk> or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit . 
 Under adverse conditions , relatively high concentrations of radioactive xenon isotopes may be found emanating from nuclear reactors due to the release of fission products from cracked fuel rods , or <unk> of uranium in cooling water . 
 Because xenon is a <unk> for two parent isotopes , xenon isotope ratios in meteorites are a powerful tool for studying the formation of the solar system . The iodine @-@ xenon method of dating gives the time <unk> between nucleosynthesis and the condensation of a solid object from the solar nebula . In 1960 , physicist John H. Reynolds discovered that certain meteorites contained an isotopic anomaly in the form of an overabundance of xenon @-@ 129 . He inferred that this was a decay product of radioactive iodine @-@ 129 . This isotope is produced slowly by cosmic ray <unk> and nuclear fission , but is produced in quantity only in supernova explosions . As the half @-@ life of 129I is comparatively short on a <unk> time scale , only 16 million years , this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the 129I . These two events ( supernova and <unk> of gas cloud ) were inferred to have happened during the early history of the Solar System , as the 129I isotope was likely generated before the Solar System was formed , but not long before , and <unk> the solar gas cloud with isotopes from a second source . This supernova source may also have caused collapse of the solar gas cloud . 
 In a similar way , xenon isotopic ratios such as 129Xe / <unk> and <unk> / <unk> are also a powerful tool for understanding planetary differentiation and early outgassing . For example , The atmosphere of Mars shows a xenon abundance similar to that of Earth : 0 @.@ 08 parts per million , however Mars shows a higher proportion of 129Xe than the Earth or the Sun . As this isotope is generated by radioactive decay , the result may indicate that Mars lost most of its primordial atmosphere , possibly within the first 100 million years after the planet was formed . In another example , excess 129Xe found in carbon dioxide well gases from New Mexico was believed to be from the decay of mantle @-@ derived gases soon after Earth 's formation . 
 
 = = Compounds = = 
 
 After Neil Bartlett 's discovery in 1962 that xenon can form chemical compounds , a large number of xenon compounds have been discovered and described . Almost all known xenon compounds contain the electronegative atoms fluorine or oxygen . 
 
 = = = Halides = = = 
 
 Three fluorides are known : XeF 
 2 , XeF 
 4 , and XeF 
 6 . XeF is theorized to be unstable . The fluorides are the starting point for the synthesis of almost all xenon compounds . 
 The solid , crystalline difluoride XeF 
 2 is formed when a mixture of fluorine and xenon gases is exposed to ultraviolet light . Ordinary daylight is sufficient . Long @-@ term heating of XeF 
 2 at high temperatures under an <unk> 
 2 catalyst yields XeF 
 6 . <unk> of XeF 
 6 in the presence of <unk> yields high @-@ purity XeF 
 4 . 
 The xenon fluorides behave as both fluoride <unk> and fluoride donors , forming salts that contain such <unk> as XeF + and Xe 
 2F + 
 3 , and anions such as XeF − 
 5 , XeF − 
 7 , and <unk> − 
 8 . The green , <unk> Xe + 
 2 is formed by the reduction of XeF 
 2 by xenon gas . 
 XeF 
 2 is also able to form coordination complexes with transition metal ions . Over 30 such complexes have been synthesized and characterized . 
 Whereas the xenon fluorides are well @-@ characterized , the other halides are not known , the only exception being the <unk> , <unk> . Xenon <unk> is reported to be an <unk> , colorless , crystalline compound that <unk> into the elements at 80 ° C , formed by the high @-@ frequency irradiation of a mixture of xenon , fluorine , and silicon or carbon <unk> . However , doubt has been raised as to whether <unk> 
 2 is a real compound and not merely a van der <unk> molecule consisting of weakly bound Xe atoms and Cl 
 2 molecules . Theoretical calculations indicate that the linear molecule <unk> 
 2 is less stable than the van der <unk> complex . 
 
 = = = <unk> and <unk> = = = 
 
 Three oxides of xenon are known : xenon trioxide ( XeO 
 3 ) and xenon tetroxide ( XeO 
 4 ) , both of which are dangerously explosive and powerful oxidizing agents , and xenon dioxide ( <unk> ) , which was reported in 2011 with a coordination number of four . <unk> forms when xenon <unk> is poured over ice . Its crystal structure may allow it to replace silicon in <unk> minerals . The <unk> + cation has been identified by infrared spectroscopy in solid argon . 
 Xenon does not react with oxygen directly ; the trioxide is formed by the hydrolysis of XeF 
 6 : 
 XeF 
 6 + 3 H 
 2O → XeO 
 3 + 6 HF 
 XeO 
 3 is weakly acidic , dissolving in alkali to form unstable <unk> salts containing the <unk> − 
 4 anion . These unstable salts easily <unk> into xenon gas and perxenate salts , containing the <unk> − 
 6 anion . 
 <unk> perxenate , when treated with concentrated sulfuric acid , yields <unk> xenon tetroxide : 
 Ba 
 <unk> 
 6 + 2 H 
 <unk> 
 4 → 2 <unk> 
 4 + 2 H 
 2O + XeO 
 4 
 To prevent decomposition , the xenon tetroxide thus formed is quickly cooled to form a pale @-@ yellow solid . It explodes above − 35 @.@ 9 ° C into xenon and oxygen gas . 
 A number of xenon <unk> are known , including XeOF 
 2 , XeOF 
 4 , XeO 
 2F 
 2 , and XeO 
 <unk> 
 2 . XeOF 
 2 is formed by the reaction of <unk> 
 2 with xenon gas at low temperatures . It may also be obtained by the partial hydrolysis of XeF 
 4 . It <unk> at − 20 ° C into XeF 
 2 and XeO 
 2F 
 2 . XeOF 
 4 is formed by the partial hydrolysis of XeF 
 6 , or the reaction of XeF 
 6 with sodium perxenate , Na 
 <unk> 
 6 . The latter reaction also produces a small amount of XeO 
 <unk> 
 2 . XeOF 
 4 reacts with <unk> to form the XeOF − 
 5 anion , while <unk> reacts with the alkali metal fluorides <unk> , <unk> and <unk> to form the XeOF − 
 4 anion . 
 
 = = = Other compounds = = = 
 
 Recently , there has been an interest in xenon compounds where xenon is directly bonded to a less electronegative element than fluorine or oxygen , particularly carbon . <unk> @-@ withdrawing groups , such as groups with fluorine substitution , are necessary to stabilize these compounds . Numerous such compounds have been characterized , including : 
 C 
 6F 
 5 – Xe + – N <unk> C – CH 
 3 , where <unk> is the <unk> group . 
 [ C 
 6F 
 5 ] 
 <unk> 
 C 
 6F 
 5 – Xe – X , where X is <unk> , F , or Cl . 
 R – C <unk> C – Xe + , where R is C 
 2F − 
 5 or <unk> @-@ butyl . 
 C 
 6F 
 5 – XeF + 
 2 
 ( C 
 6F 
 <unk> ) 
 <unk> + 
 Other compounds containing xenon bonded to a less electronegative element include F – Xe – N ( <unk> 
 2F ) 
 2 and F – Xe – <unk> 
 2 . The latter is synthesized from <unk> <unk> , O 
 <unk> 
 4 , at − 100 ° C. 
 An unusual ion containing xenon is the <unk> ( II ) cation , <unk> + 
 4 , which contains Xe – <unk> bonds . This ion occurs in the compound <unk> 
 4 ( Sb 
 2F 
 11 ) 
 2 , and is remarkable in having direct chemical bonds between two notoriously <unk> atoms , xenon and gold , with xenon acting as a transition metal ligand . 
 The compound Xe 
 <unk> 
 2F 
 11 contains a Xe – Xe bond , the longest element @-@ element bond known ( 308 @.@ 71 pm = 3 @.@ <unk> <unk> ) . 
 In 1995 , M. <unk> and co @-@ workers , scientists at the University of Helsinki in Finland , announced the preparation of xenon <unk> ( <unk> ) , and later xenon hydride @-@ hydroxide ( <unk> ) , <unk> ( <unk> ) , and other Xe @-@ containing molecules . In 2008 , <unk> et al. reported the preparation of <unk> by the <unk> of water within a <unk> xenon matrix . <unk> molecules , <unk> and <unk> , have also been produced . 
 
 = = = <unk> and <unk> = = = 
 
 In addition to compounds where xenon forms a chemical bond , xenon can form <unk> — substances where xenon atoms or pairs are trapped by the crystalline lattice of another compound . One example is xenon hydrate ( Xe <unk> 5 @.@ 75 H2O ) , where xenon atoms occupy vacancies in a lattice of water molecules . This <unk> has a melting point of 24 ° C. The <unk> version of this hydrate has also been produced . Another example is Xe hydride ( Xe ( H2 ) 8 ) , in which xenon pairs ( <unk> ) are trapped inside solid hydrogen . Such <unk> <unk> can occur naturally under conditions of high pressure , such as in Lake <unk> underneath the Antarctic ice sheet . <unk> formation can be used to <unk> <unk> xenon , argon and krypton . 
 Xenon can also form <unk> fullerene compounds , where a xenon atom is trapped inside a fullerene molecule . The xenon atom trapped in the fullerene can be monitored via 129Xe nuclear magnetic resonance ( NMR ) spectroscopy . Using this technique , chemical reactions on the fullerene molecule can be analyzed , due to the sensitivity of the chemical shift of the xenon atom to its environment . However , the xenon atom also has an electronic influence on the reactivity of the fullerene . 
 When xenon atoms are at their ground energy state , they repel each other and will not form a bond . When xenon atoms becomes <unk> , however , they can form an excimer ( excited dimer ) until the electrons return to the ground state . This entity is formed because the xenon atom tends to fill its outermost electronic shell , and can briefly do this by adding an electron from a neighboring xenon atom . The typical lifetime of a xenon excimer is 1 – 5 <unk> , and the decay releases photons with <unk> of about 150 and 173 nm . Xenon can also form <unk> with other elements , such as the <unk> <unk> , chlorine and fluorine . 
 
 = = Applications = = 
 
 Although xenon is rare and relatively expensive to extract from the Earth 's atmosphere , it has a number of applications . 
 
 = = = <unk> and optics = = = 
 
 
 = = = = Gas @-@ discharge lamps = = = = 
 
 Xenon is used in light @-@ emitting devices called xenon flash lamps , which are used in photographic flashes and <unk> lamps ; to excite the active medium in lasers which then generate coherent light ; and , occasionally , in <unk> lamps . The first solid @-@ state laser , invented in 1960 , was pumped by a xenon flash lamp , and lasers used to power <unk> confinement fusion are also pumped by xenon flash lamps . 
 <unk> , short @-@ arc , high pressure xenon arc lamps have a color temperature closely <unk> noon sunlight and are used in solar simulators . That is , the <unk> of these lamps closely <unk> a heated black body <unk> that has a temperature close to that observed from the Sun . After they were first introduced during the 1940s , these lamps began replacing the shorter @-@ lived carbon arc lamps in movie <unk> . They are employed in typical 35mm , <unk> and the new digital <unk> film projection systems , automotive <unk> <unk> , high @-@ end " tactical " <unk> and other specialized uses . These arc lamps are an excellent source of short wavelength ultraviolet radiation and they have intense emissions in the near infrared , which is used in some night vision systems . 
 The individual cells in a plasma display use a mixture of xenon and neon that is converted into a plasma using electrodes . The interaction of this plasma with the electrodes generates ultraviolet photons , which then excite the phosphor coating on the front of the display . 
 Xenon is used as a " starter gas " in high pressure sodium lamps . It has the lowest thermal <unk> and lowest ionization potential of all the non @-@ radioactive noble gases . As a noble gas , it does not interfere with the chemical reactions occurring in the operating lamp . The low thermal <unk> <unk> thermal losses in the lamp while in the operating state , and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state , which allows the lamp to be more easily started . 
 
 = = = = <unk> = = = = 
 
 In 1962 , a group of researchers at Bell Laboratories discovered laser action in xenon , and later found that the laser gain was improved by adding helium to the <unk> medium . The first excimer laser used a xenon dimer ( <unk> ) <unk> by a beam of electrons to produce stimulated emission at an ultraviolet wavelength of 176 nm . Xenon chloride and xenon fluoride have also been used in excimer ( or , more accurately , <unk> ) lasers . The xenon chloride excimer laser has been employed , for example , in certain <unk> uses . 
 
 = = = Medical = = = 
 
 
 = = = = <unk> = = = = 
 
 Xenon has been used as a general anesthetic . Although it is expensive , anesthesia machines that can deliver xenon are about to appear on the European market , because advances in recovery and recycling of xenon have made it economically viable . 
 Xenon interacts with many different receptors and ion channels and like many theoretically multi @-@ modal inhalation <unk> these interactions are likely complementary . Xenon is a high @-@ affinity <unk> @-@ site NMDA receptor antagonist . However , xenon distinguishes itself from other clinically used NMDA receptor antagonists in its lack of <unk> and its ability to inhibit the <unk> of <unk> and nitrous oxide . Unlike <unk> and nitrous oxide , xenon does not stimulate a <unk> <unk> in the nucleus <unk> . Like nitrous oxide and <unk> , xenon activates the two @-@ pore domain potassium channel <unk> @-@ 1 . A related channel <unk> @-@ 3 also implicated in <unk> anesthetic actions is insensitive to xenon . Xenon inhibits <unk> acetylcholine <unk> receptors which contribute to <unk> mediated <unk> . Xenon is an effective inhibitor of plasma membrane Ca2 + <unk> . Xenon inhibits Ca2 + <unk> by binding to a hydrophobic pore within the enzyme and preventing the enzyme from assuming active conformations . 
 Xenon is a competitive inhibitor of the <unk> 5 @-@ <unk> receptor . While neither anesthetic nor <unk> this activity reduces anesthesia @-@ <unk> nausea and vomiting . 
 Xenon has a minimum <unk> concentration ( <unk> ) of 72 % at age 40 , making it 44 % more potent than <unk> as an anesthetic . Thus it can be used in concentrations with oxygen that have a lower risk of hypoxia . Unlike nitrous oxide ( <unk> ) , xenon is not a <unk> gas and so it is also viewed as environmentally friendly . Xenon vented into the atmosphere is being returned to its original source , so no environmental impact is likely . 
 
 = = = = <unk> = = = = 
 
 Xenon <unk> robust <unk> and <unk> through a variety of mechanisms of action . Through its influence on Ca2 + , K + , <unk> \ <unk> and NMDA <unk> xenon is <unk> when administered before , during and after ischemic insults . Xenon is a high affinity antagonist at the NMDA receptor <unk> site . Xenon is <unk> in <unk> @-@ <unk> conditions by inducing <unk> non @-@ ischemic <unk> . Xenon is <unk> by activating <unk> @-@ <unk> & downstream <unk> @-@ <unk> . Xenon <unk> <unk> ischemic <unk> by activating ATP sensitive potassium channels . Xenon <unk> reduces ATP mediated channel activation <unk> independently of the <unk> <unk> <unk> , increasing <unk> open @-@ channel time and frequency . Xenon <unk> hypoxia <unk> factor 1 alpha ( <unk> ) . 
 Xenon gas was added as an ingredient of the ventilation mix for a newborn baby at St. Michael 's Hospital , Bristol , England , whose life chances were otherwise very compromised , and was successful , leading to the <unk> of clinical trials for similar cases . The treatment is done simultaneously with cooling the body temperature to 33 @.@ 5 ° C. 
 
 = = = = Doping = = = = 
 
 <unk> a xenon / oxygen mixture activates production of the transcription factor <unk> @-@ 1 @-@ alpha , which leads to increased production of <unk> . The latter hormone is known to increase red blood cell production and athletes ' performance . Xenon inhalation has been used for this purpose in Russia since at least 2004 . On August 31 2014 the World Anti Doping Agency ( <unk> ) added Xenon ( and <unk> ) to the list of prohibited substances and methods , although at this time there is no reliable drug test . 
 
 = = = = Imaging = = = = 
 
 <unk> emission from the <unk> 133Xe of xenon can be used to image the heart , lungs , and brain , for example , by means of single <unk> emission computed <unk> . 133Xe has also been used to measure blood flow . 
 Xenon , particularly <unk> 129Xe , is a useful contrast agent for magnetic resonance imaging ( <unk> ) . In the gas phase , it can be used to image empty space such as cavities in a porous sample or <unk> in lungs . <unk> renders 129Xe much more detectable via magnetic resonance imaging and has been used for studies of the lungs and other tissues . It can be used , for example , to trace the flow of gases within the lungs . Because xenon is soluble in water and also in hydrophobic <unk> , it can be used to image various soft living tissues . 
 
 = = = NMR spectroscopy = = = 
 
 Because of the xenon atom 's large , flexible outer electron shell , the NMR spectrum changes in response to surrounding conditions , and can therefore be used as a probe to measure the chemical circumstances around it . For instance xenon dissolved in water , xenon dissolved in hydrophobic solvent , and xenon associated with certain proteins can be distinguished by NMR . 
 <unk> xenon can be used by surface <unk> . Normally , it is difficult to characterize surfaces using NMR , because signals from the surface of a sample will be overwhelmed by signals from the far @-@ more @-@ numerous atomic nuclei in the bulk . However , nuclear spins on solid surfaces can be selectively polarized , by transferring spin polarization to them from <unk> xenon gas . This makes the surface signals strong enough to measure , and distinguishes them from bulk signals . 
 
 = = = Other = = = 
 
 In nuclear energy applications , xenon is used in bubble chambers , probes , and in other areas where a high molecular weight and inert nature is desirable . A by @-@ product of nuclear weapon testing is the release of radioactive xenon @-@ 133 and xenon @-@ 135 . The detection of these isotopes is used to monitor compliance with nuclear test ban treaties , as well as to confirm nuclear test explosions by states such as North Korea . 
 Liquid xenon is being used in <unk> for measurements of gamma rays as well as a medium for detecting hypothetical weakly interacting massive particles , or <unk> . When a <unk> <unk> with a xenon nucleus , it is predicted to <unk> enough energy to cause ionization and <unk> . Liquid xenon is useful for this type of experiment due to its high density which makes dark matter interaction more likely and permits a quiet detector due to self @-@ shielding . 
 Xenon is the preferred propellant for ion propulsion of spacecraft because of its low ionization potential per atomic weight , and its ability to be stored as a liquid at near room temperature ( under high pressure ) yet be easily converted back into a gas to feed the engine . The inert nature of xenon makes it environmentally friendly and less corrosive to an ion engine than other fuels such as mercury or caesium . Xenon was first used for satellite ion engines during the 1970s . It was later employed as a propellant for <unk> 's Deep Space 1 probe , Europe 's <unk> @-@ 1 spacecraft and for the three ion propulsion engines on NASA 's Dawn <unk> . 
 <unk> , the perxenate compounds are used as oxidizing agents in analytical chemistry . Xenon difluoride is used as an <unk> for silicon , particularly in the production of <unk> systems ( <unk> ) . The <unk> drug 5 @-@ <unk> can be produced by reacting xenon difluoride with <unk> . Xenon is also used in protein crystallography . Applied at pressures from 0 @.@ 5 to 5 MPa ( 5 to 50 <unk> ) to a protein crystal , xenon atoms bind in predominantly hydrophobic cavities , often creating a high @-@ quality , <unk> , heavy @-@ atom derivative , which can be used for solving the phase problem . 
 
 = = Precautions = = 
 
 Many oxygen @-@ containing xenon compounds are toxic due to their strong <unk> properties , and explosive due to their tendency to break down into elemental xenon plus <unk> oxygen ( O2 ) , which contains much stronger chemical bonds than the xenon compounds . 
 Xenon gas can be safely kept in normal sealed glass or metal containers at standard temperature and pressure . However , it readily dissolves in most <unk> and rubber , and will gradually escape from a container sealed with such materials . Xenon is non @-@ toxic , although it does dissolve in blood and belongs to a select group of substances that penetrate the blood – brain barrier , causing mild to full surgical anesthesia when inhaled in high concentrations with oxygen . 
 At 169 m / s , the speed of sound in xenon gas is lower than that in air due to the lower average speed of the heavy xenon atoms compared to nitrogen and oxygen molecules . Hence , xenon lowers the rate of vibration in the vocal tract when exhaled . This produces a characteristic lowered voice <unk> , an effect opposite to the high @-@ <unk> voice caused by inhalation of helium . Like helium , xenon does not satisfy the body 's need for oxygen . Xenon is both a simple <unk> and an anesthetic more powerful than nitrous oxide ; consequently , many universities no longer allow the voice stunt as a general chemistry demonstration . As xenon is expensive , the gas sulfur hexafluoride , which is similar to xenon in molecular weight ( 146 versus 131 ) , is generally used in this stunt , and is an <unk> without being anesthetic . 
 It is possible to safely <unk> dense gases such as xenon or sulfur hexafluoride when they are in a mixture of at least 20 % oxygen . Xenon at 80 % concentration along with 20 % oxygen rapidly produces the unconsciousness of general anesthesia ( and has been used for this , as discussed above ) . <unk> mixes gases of different densities very effectively and rapidly so that heavier gases are purged along with the oxygen , and do not accumulate at the bottom of the lungs . There is , however , a danger associated with any heavy gas in large quantities : it may sit <unk> in a container , and if a person enters a container filled with an <unk> , colorless gas , they may find themselves breathing it unknowingly . Xenon is rarely used in large enough quantities for this to be a concern , though the potential for danger exists any time a tank or container of xenon is kept in an <unk> space . 
 
 