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= = Death and legacy = =
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Berhtwald died on 13 January 731 . An epitaph to him in verse survives , and may have been placed over his tomb , which was at Canterbury . Subsequently he was canonised with a feast day of 9 January . Little evidence of extensive cult activity exists , however , and the main evidence for his sainthood is a late medieval entry in a St Augustine 's calendar . Berhtwald is the first of the continuous series of native @-@ born archbishops in England , although there had been two previous Anglo @-@ Saxon archbishops at Canterbury — Deusdedit and Wighard .
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= Xenon =
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Xenon is a chemical element with symbol Xe and atomic number 54 . It is a colorless , dense , odorless noble gas , that occurs in the Earth 's atmosphere in trace amounts . Although generally unreactive , xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate , the first noble gas compound to be synthesized .
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Xenon is used in flash lamps and arc lamps , and as a general anesthetic . The first excimer laser design used a xenon dimer molecule ( Xe2 ) as its lasing 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 thrusters in spacecraft .
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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 . Radioactive 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 absorber in nuclear reactors .
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= = History = =
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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 evaporating components of liquid air . Ramsay suggested the name xenon for this gas from the Greek word ξένον [ xenon ] , neuter singular form of ξένος [ xenos ] , 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 .
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During the 1930s , American engineer Harold Edgerton began exploring strobe 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 , Edgerton was able to generate flashes as brief as one microsecond with this method .
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In 1939 , American physician Albert R. Behnke Jr. began exploring the causes of " drunkenness " 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 toxicologist Nikolay V. Lazarev 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 anesthesiologist Stuart C. Cullen , who successfully operated on two patients .
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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 oxidize oxygen gas ( O2 ) to form dioxygenyl hexafluoroplatinate ( O2 + [ PtF6 ] − ) . Since O2 and xenon have almost the same first ionization potential , Bartlett realized that platinum hexafluoride might also be able to oxidize 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 radon , including argon fluorohydride ( HArF ) , krypton difluoride ( KrF2 ) , and radon fluoride . By 1971 , more than 80 xenon compounds were known .
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In November 1999 IBM scientists demonstrated a technology capable of manipulating individual atoms . The program , called IBM in atoms , used a scanning tunneling microscope to arrange 35 individual xenon atoms on a substrate of chilled 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 .
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= = Characteristics = =
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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 / mL , with the density maximum occurring at the triple point . Notably , liquid xenon has a high polarizability due to its large atomic volume , and thus is an excellent solvent . It can dissolve hydrocarbons , 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 gigapascals of pressure , xenon has been forced into a metallic phase .
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Solid xenon changes from face @-@ centered cubic ( fcc ) to hexagonal close packed ( hcp ) crystal phase under pressure and begins to turn metallic at about 140 GPa , with no noticeable volume change in the hcp phase . It is completely metallic at 155 GPa . When metallized , xenon looks sky blue because it absorbs red light and transmits 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 .
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Liquid or solid xenon nanoparticles can be formed at room temperature by implanting Xe + ions into a solid matrix . Many solids have lattice constants smaller than solid Xe . This results in compression of the implanted Xe to pressures that may be sufficient for its liquefaction or solidification .
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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 .
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In a gas @-@ filled tube , xenon emits a blue or lavenderish 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 .
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= = Occurrence and production = =
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Xenon is a trace gas in Earth 's atmosphere , occurring at 87 ± 1 parts per billion ( nL / L ) , or approximately 1 part per 11 @.@ 5 million , and is also found as a component in gases emitted from some mineral springs .
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Xenon is obtained commercially as a by @-@ product of the separation of air into oxygen and nitrogen . After this separation , generally performed by fractional distillation in a double @-@ column plant , the liquid oxygen produced will contain small quantities of krypton and xenon . By additional fractional 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 silica 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 liter .
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Within the Solar System , the nucleon 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 planetesimals — small , subplanetary bodies — before the presolar disk began to heat up . ( Otherwise , xenon would not have been trapped in the planetesimal ices . ) The problem of the low terrestrial xenon may potentially be explained by covalent bonding of xenon to oxygen within quartz , hence reducing the outgassing of xenon into the atmosphere .
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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 .
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= = Isotopes and isotopic studies = =
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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 124Xe and 134Xe 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 136Xe , which has been observed to undergo double beta decay with a half @-@ life of 2 @.@ 11 × 1021 yr . 129Xe is produced by beta decay of 129I , which has a half @-@ life of 16 million years , while 131mXe , 133Xe , 133mXe , and 135Xe are some of the fission products of both 235U and 239Pu , and therefore used as indicators of nuclear explosions .
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Nuclei of two of the stable isotopes of xenon , 129Xe and 131Xe , have non @-@ zero intrinsic angular momenta ( nuclear spins , suitable for nuclear magnetic resonance ) . The nuclear spins can be aligned beyond ordinary polarization levels by means of circularly polarized light and rubidium vapor . The resulting spin polarization of xenon nuclei can surpass 50 % of its maximum possible value , greatly exceeding the thermal equilibrium value dictated by paramagnetic 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 hyperpolarization . The process of hyperpolarizing the xenon is called optical pumping ( although the process is different from pumping a laser ) .
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Because a 129Xe nucleus has a spin of 1 / 2 , and therefore a zero electric quadrupole moment , the 129Xe nucleus does not experience any quadrupolar interactions during collisions with other atoms , and thus its hyperpolarization 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 , 131Xe has a nuclear spin value of 3 ⁄ 2 and a nonzero quadrupole moment , and has t1 relaxation times in the millisecond and second ranges .
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Some radioactive isotopes of xenon , for example , 133Xe and 135Xe , are produced by neutron irradiation of fissionable 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 barns , so it acts as a neutron absorber 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 Chernobyl disaster . A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit .
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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 fissioning of uranium in cooling water .
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Because xenon is a tracer 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 elapsed 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 spallation and nuclear fission , but is produced in quantity only in supernova explosions . As the half @-@ life of 129I is comparatively short on a cosmological 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 solidification 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 seeded the solar gas cloud with isotopes from a second source . This supernova source may also have caused collapse of the solar gas cloud .
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In a similar way , xenon isotopic ratios such as 129Xe / 130Xe and 136Xe / 130Xe 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 .
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= = Compounds = =
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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 .
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= = = Halides = = =
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Three fluorides are known : XeF
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2 , XeF
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4 , and XeF
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6 . XeF is theorized to be unstable . The fluorides are the starting point for the synthesis of almost all xenon compounds .
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The solid , crystalline difluoride XeF
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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
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2 at high temperatures under an NiF
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2 catalyst yields XeF
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6 . Pyrolysis of XeF
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6 in the presence of NaF yields high @-@ purity XeF
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4 .
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The xenon fluorides behave as both fluoride acceptors and fluoride donors , forming salts that contain such cations as XeF + and Xe
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2F +
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3 , and anions such as XeF −
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5 , XeF −
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7 , and XeF2 −
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8 . The green , paramagnetic Xe +
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2 is formed by the reduction of XeF
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2 by xenon gas .
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XeF
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2 is also able to form coordination complexes with transition metal ions . Over 30 such complexes have been synthesized and characterized .
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Whereas the xenon fluorides are well @-@ characterized , the other halides are not known , the only exception being the dichloride , XeCl2 . Xenon dichloride is reported to be an endothermic , colorless , crystalline compound that decomposes into the elements at 80 ° C , formed by the high @-@ frequency irradiation of a mixture of xenon , fluorine , and silicon or carbon tetrachloride . However , doubt has been raised as to whether XeCl
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2 is a real compound and not merely a van der Waals molecule consisting of weakly bound Xe atoms and Cl
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2 molecules . Theoretical calculations indicate that the linear molecule XeCl
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2 is less stable than the van der Waals complex .
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= = = Oxides and oxohalides = = =
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Three oxides of xenon are known : xenon trioxide ( XeO
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3 ) and xenon tetroxide ( XeO
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4 ) , both of which are dangerously explosive and powerful oxidizing agents , and xenon dioxide ( XeO2 ) , which was reported in 2011 with a coordination number of four . XeO2 forms when xenon tetrafluoride is poured over ice . Its crystal structure may allow it to replace silicon in silicate minerals . The XeOO + cation has been identified by infrared spectroscopy in solid argon .
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Xenon does not react with oxygen directly ; the trioxide is formed by the hydrolysis of XeF
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6 :
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XeF
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6 + 3 H
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2O → XeO
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3 + 6 HF
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XeO
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3 is weakly acidic , dissolving in alkali to form unstable xenate salts containing the HXeO −
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4 anion . These unstable salts easily disproportionate into xenon gas and perxenate salts , containing the XeO4 −
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6 anion .
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Barium perxenate , when treated with concentrated sulfuric acid , yields gaseous xenon tetroxide :
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Ba
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2XeO
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6 + 2 H
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2SO
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4 → 2 BaSO
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4 + 2 H
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2O + XeO
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4
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