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Cresswell joined First Division club Preston North End on loan for the remainder of the 2000 β 01 season on 10 March 2001 and scored five minutes into his debut , a 2 β 0 win at home to Wolverhampton Wanderers on 14 March . He came on as an 82nd minute substitute in their 3 β 0 defeat to Bolton Wanderers in the 2001 First Division play @-@ off Final at the Millennium Stadium on 28 May 2001 . After scoring two goals in 14 appearances he signed for Preston permanently on a four @-@ year contract for a fee of Β£ 500 @,@ 000 on 14 July 2001 . |
Cresswell was Preston 's top scorer in his first two permanent seasons with Preston , scoring 15 goals in 44 appearances in 2001 β 02 and scoring 16 in 46 games in 2002 β 03 . He was also named Preston 's Player of the Year for the 2001 β 02 season . He received the first red card of his career in Preston 's 4 β 1 defeat away at Coventry City on 17 March 2004 after he was judged to have kicked out at opponent player Calum Davenport , although both managers later admitted David Healy was the culprit . He scored three goals in 47 appearances in the 2003 β 04 season . |
Cresswell drew praise from manager Billy Davies during the 2004 β 05 season , " Richard is very capable of that and it is important that we keep creating chances for Cressy as we know that he will put the ball in the back of the net " , although he admitted the team were over reliant on Cresswell 's goals . He enjoyed his best goal return in the 2004 β 05 season , top scoring for Preston with 21 goals in 52 games . This helped Preston reach the 2005 Championship play @-@ off Final , where they were beaten 1 β 0 by West Ham United at the Millennium Stadium . Cresswell played poorly in the first half , but had a number of chances on goal during the second half . |
= = = Leeds United = = = |
Cresswell was bought by Championship rivals Leeds United on a four @-@ year contract on 24 August 2005 for a fee of Β£ 1 @.@ 15 million , after rivals Sheffield United had a Β£ 1 million bid accepted . After the signing was completed , manager Kevin Blackwell said " To get a player of Cresswell 's quality is amazing " , while Cresswell cited his desire to win automatic promotion with Leeds . He first found the net with two goals in Leeds ' League Cup 2 β 0 away victory against Rotherham United on 20 September 2005 . However , Cresswell suffered knee ligament damage in a match against Derby County eight days later . This injury kept Cresswell out of action for seven weeks , making his return in Leeds ' 1 β 0 defeat away to Wolves on 17 December 2005 , and scoring in his second match back against Coventry City in a 3 β 1 home win on 26 December . Another knee injury picked up during a training session in February 2006 kept him out of the team until he entered Leeds ' 1 β 1 draw with former club Preston in the Championship play @-@ off semi @-@ final first leg as a 78th @-@ minute substitute on 5 May 2006 . However , he was sent off in the 2 β 0 win in the second leg , meaning he was suspended for the 2006 Championship play @-@ off Final , which Leeds lost 3 β 0 to Watford at the Millennium Stadium . He finished the 2005 β 06 season with 21 appearances and seven goals . |
Having damaged his knee ligaments during the play @-@ off semi @-@ final , Cresswell missed the start of the 2006 β 07 season , making his first appearance in Leeds ' 4 β 0 home defeat to Stoke City on 14 October 2006 . However , he sustained a knee injury in November 2006 , after scoring his first goal of the campaign in Leeds ' 3 β 0 home win over Colchester United on 11 November . His return from injury came as a 68th @-@ minute substitute in a 2 β 1 victory at home to Crystal Palace on 10 February 2007 . Cresswell scored in successive games against Sheffield Wednesday and Luton Town in March 2007 , but Leeds were eventually relegated to League One . He finished the season with four goals in 23 games . |
= = = Stoke City = = = |
Leeds were resigned to losing their senior players after going into administration , with Championship side Stoke City signing Cresswell on a three @-@ year contract for an undisclosed fee on 2 August 2007 , after Hull City had pulled out of a deal after expressing concerns following his medical . He made his debut in a 1 β 0 win at Cardiff City on 11 August 2007 , before scoring in his second appearance with an equaliser during stoppage time of extra time in a 2 β 2 draw away to Rochdale in the League Cup first round on 14 August , although Stoke lost 4 β 2 in a penalty shoot @-@ out . He scored the last ever goal at Colchester United 's Layer Road ground in a 1 β 0 win . Cresswell made 46 appearances for Stoke in the 2007 β 08 season , scoring 12 goals , as the club won promotion the Premier League as Championship runners @-@ up . He was regularly used on the left wing by Stoke manager Tony Pulis , even though his natural position is as a striker . He was quoted as saying he enjoyed playing as a winger , saying " I do my best , and I am quite a fit lad so I get through quite a bit of mileage " . During the 2008 β 09 season Cresswell played on the wing and as a striker , featuring in 34 games and scoring one goal . |
= = = Sheffield United = = = |
Having struggled for appearances with Stoke since their promotion to the Premier League , Cresswell joined Championship outfit Sheffield United on a three @-@ month loan on 29 September 2009 and made his debut the same day as a 76th @-@ minute substitute against Ipswich Town in a 3 β 3 home draw . Starting the following game he scored a 65th @-@ minute equaliser against Doncaster Rovers in a 1 β 1 draw at home on 3 October 2009 . He joined United permanently on a one @-@ and @-@ a @-@ half @-@ year contract for an undisclosed fee on 5 January 2010 , going on to finish the 2009 β 10 season as top scorer with 14 goals . He was rewarded with a new three @-@ year contract with the club in June 2010 . He scored five goals in 36 games in the 2010 β 11 season as United were relegated to League One . |
With United now in League One , Cresswell formed a striking partnership with Ched Evans , making 51 appearances and scoring 10 goals in 2011 β 12 . The club failed to achieve promotion however , being beaten 8 β 7 in a penalty shoot @-@ out by Huddersfield Town in the 2012 League One play @-@ off Final at Wembley Stadium on 26 May 2012 , in which Cresswell was substituted for Chris Porter in the 85th minute . As a result of financial circumstances Cresswell and Nick Montgomery were made available for transfer during August 2012 , with manager Danny Wilson explaining that " They were both fit , they were left out for financial reasons " . Towards the end of the transfer window however United agreed a revised deal to change his role to that of player @-@ coach and as such he would be remaining at Bramall Lane for the foreseeable future . On his return to the side , Cresswell came on as a substitute and scored a header in United 's 5 β 3 victory over Bournemouth on 1 September 2012 . |
= = = Return to York City = = = |
Cresswell rejoined his first club York City , playing in League Two , on a one @-@ month loan on 19 March 2013 . He marked his second York debut by scoring a 73rd minute penalty kick on 23 March 2013 away at Torquay United in a 2 β 1 defeat . He played an important role as York fought against relegation , scoring twice in five appearances , before being recalled by new United caretaker manager Chris Morgan on 15 April 2013 . In July 2013 new United manager David Weir stated that Cresswell would be leaving the club , before he signed for York permanently on a one @-@ year contract on 16 July 2013 . His first appearance after signing permanently came in the first game of the 2013 β 14 season , a 1 β 0 home win over Northampton Town on 3 August 2013 . Cresswell retired from playing on 5 December 2013 , as a result of an eye complaint and a knee injury . He made eight appearances for York in the 2013 β 14 season . |
= = International career = = |
Cresswell was called up to the England national under @-@ 21 team while with York , making his debut in a 2 β 1 home victory over France in a friendly on 9 February 1999 . He continued to play for the under @-@ 21s after joining Wednesday , and scored his first goal for them in a 3 β 0 home win over Sweden in a 2000 UEFA European Under @-@ 21 Championship qualification match on 4 June 1999 . Cresswell finished his under @-@ 21 career with four caps and one goal . |
= = Coaching career = = |
Cresswell returned to York as a commercial , academy and community development consultant in April 2014 , having previously intended to pursue a career in coaching . He took on the position of Head of Football Operations , before being appointed as first team coach to manager Russ Wilcox in March 2015 . In May 2015 , Cresswell resumed his role as Head of Football Operations , while continuing to coach the first team . He took over as caretaker manager on 26 October 2015 after Wilcox 's sacking , and would be assisted by youth team coach Jonathan Greening and goalkeeping coach Andy Leaning . He was in charge for the 1 β 0 away defeat to Crawley Town on 31 October 2015 , before ceasing his caretaker duties upon the appointment of Jackie McNamara as manager on 4 November . Cresswell left York by mutual consent on 16 December 2015 . He resumed his playing career aged 38 when signing for Northern Counties East League Premier Division club Tadcaster Albion on 7 April 2016 . |
= = Personal life = = |
Cresswell married Zoe Chapman at Christ Church , Bridlington on 7 June 2003 , with former York City teammate Jonathan Greening being his joint best man . He took part in a 170 mile bike ride during 2012 to raise money for a charity which helps children with Dravet 's syndrome , after his twin nieces were diagnosed with the disorder . |
= = Career statistics = = |
As of match played 14 April 2016 . |
= = Managerial statistics = = |
As of 4 November 2015 . |
= = Honours = = |
Stoke City |
Football League Championship runner @-@ up : 2007 β 08 |
Individual |
Preston North End Player of the Year : 2001 β 02 |
= Berhtwald = |
Berhtwald ( also Brihtwald , Beorhtweald , Bertwald , Berthwald , Beorhtwald , or Beretuald ; died 731 ) was the ninth Archbishop of Canterbury in England . Documentary evidence names Berhtwald as abbot at Reculver before his election as archbishop . Berhtwald begins the first continuous series of native @-@ born Archbishops of Canterbury , although there had been previous Anglo @-@ Saxon archbishops , they had not succeeded each other until Berhtwald 's reign . |
Berhtwald 's period as archbishop coincided with the end of Wilfrid 's long struggle to regain the Bishopric of York , and the two @-@ year delay between Theodore 's death and Berhtwald 's election may have been due to efforts to select Wilfrid for Canterbury . After his election , Berhtwald went to Gaul for consecration and then presided over two councils that attempted to settle the Wilfrid issue , finally succeeding at the second council in 705 . Berhtwald also was the recipient of the first surviving letter close in Western Europe . |
= = Early life = = |
Little is known of Berhtwald 's ancestry or his early life , but he was born around the middle of the seventh century . By 679 , he was made abbot of the monastery at Reculver in Kent , and a charter dated May 679 names Berhtwald as abbot . This charter , from Hlothere , King of Kent , is the earliest surviving original Anglo @-@ Saxon charter . |
= = Election as archbishop = = |
The see of Canterbury was vacant for two years after the death of Theodore before Berhtwald was elected to the office on 1 July 692 . The long vacancy resulted from the disturbed conditions in the kingdom of Kent at the time , as various kings fought for control . The succession to the kingdom was disputed between rival claimants Oswine and Wihtred , and various outside kings , including Caedwalla and Swaefheard raided and plundered Kent . Eventually , Wihtred secured the throne , around 691 or early 692 , as Bede names Wihtred as King of Kent , along with Swaefheard , at the time of Berhtwald 's election . Swaerfheard , however , is not named as king of Kent after this date . |
The vacancy may also have occurred because Wilfrid , who was at that point having problems in Northumbria , desired to become Archbishop of Canterbury . A contemporary biographer of Wilfrid , Stephen of Ripon , says that Theodore had wished for Wilfrid to succeed Theodore at Canterbury . Γthelred of Mercia may have supported Wilfrid 's translation to Canterbury also , but despite these desires , the translation did not happen . Berhtwald was consecrated on 29 June 693 , having travelled to France for his consecration as archbishop of Canterbury by Godwin , Archbishop of Lyon . Berhtwald went to the continent for consecration probably because he feared that his election was not supported by all of the kings and bishops . After his consecration , Berhtwald travelled to Rome to obtain the support of Pope Sergius I , who wrote to a number of Anglo @-@ Saxon kings and bishops in support of the archbishop . Two of these letters survive , and their authenticity has been doubted , mainly because they are only preserved as part of the post @-@ Norman Conquest Canterbury @-@ York dispute . Historians have since come to regard the two letters as genuine . Sergius also gave Berhtwald a pallium , the symbol of an archbishop 's authority . |
= = Archbishop = = |
Berhtwald appears to have been involved in the governance of the church , establishing the bishopric of Sherborne in Wessex and it was during his tenure that Sussex , the last pagan kingdom in England , was converted to Christianity . He also consecrated the first Bishop of Selsey . During his time in office , King Wihtred of Kent in the Law of Wihtred exempted the church from taxation . Berhtwald was a proponent of his predecessor 's view of the archbishops of Canterbury as primates of the entire island of Britain . Berhtwald co @-@ operated closely with Wihtred in the kingdom , and secured the exemption of the church from taxation under Wihtred 's laws issued in 695 . The law code also dealt with other ecclesiastical matters , including marriage , Sunday observance , and pagan worship . This law code resulted from a royal council that was held at Bearsted . Further privileges for the church were issued in 699 , and may have been composed by Berhtwald before being promulgated . Another privilege , usually referred to as the " Privilege of Wihtred " , is claimed to be a grant from Wihtred to the monasteries of Kent of exemption from non @-@ clerical control . However , this is actually a ninth @-@ century forgery . |
Much of Berhtwald 's time in office coincided with the efforts of Wilfrid to regain the see of York , and to reverse the division of York into smaller dioceses . Berhtwald was opposed to Wilfrid 's desire to restore some separated bishoprics to the bishopric of York as well as regaining his old see . Wilfrid 's problems had begun during the archbishopric of Berhtwald 's predecessor , Theodore of Tarsus , when Wilfrid had quarreled with the King of Northumbria , Ecgfrith , and was expelled from the north . Theodore had taken the opportunity to divide the large see of York into a number of smaller dioceses , and Wilfrid had appealed to the papacy in Rome . Berhtwald inherited the dispute and presided at the Council of Austerfield in 702 , at which Wilfrid 's biographer relates the story that King Aldfrith of Northumbria , Berhtwald , and the other enemies of Wilfrid conspired to deprive Wilfrid of all his offices and possessions . A more likely story is that Berhtwald managed to secure concessions from the Northumbrians , and tried to broker a compromise . The offer in the end was that Wilfrid would retire to Ripon and cease acting as a bishop . Wilfrid rejected this compromise and once more appealed to the pope . Three years later , at a further Council , it was arranged that Wilfrid should receive the Bishopric of Hexham in place of that of York . This was the Council of Nidd , usually dated to 706 , and it was held in Northumbria . Bede also mentions that Berhtwald consecrated a number of bishops , including Tobias as Bishop of Rochester . |
One of Berhtwald 's letters has been preserved , sent to Forthhere , Bishop of Sherborne , and asking Forthhere to intercede with Beorwold , the Abbot of Glastonbury , to ransom a slave . Another letter , this one addressed to Berhtwald , from Waldhere , Bishop of London , also survives . The main interest in the second letter is that it is the oldest surviving letter close surviving in Western Europe . This second letter also relates that Waldhere and Berhtwald had attended a synod which can be dated to sometime between 703 and 705 , where the kingdom of Wessex was threatened with excommunication . A charter witnessed by Berhtwald which mentions a supposed 706 council , numbered 54 by Sawyer , is now known to be a fake , although the witness list may be based on a legitimate 8th century charter that no longer survives . Likewise , a charter with Berhtwald as a witness and relating to the 716 Council of Clofesho is also known to be a 9th @-@ century forgery , although again it may have been based on actual documents from the council . |
= = Death and legacy = = |
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 β Deusdedit and Wighard . |
= Xenon = |
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 . |
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 . |
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 . |
= = 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 evaporating components of liquid air . Ramsay suggested the name xenon for this gas from the Greek word ΞΎΞΞ½ΞΏΞ½ [ xenon ] , neuter singular form of ΞΎΞΞ½ΞΏΟ [ 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 . |
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 . |
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 . |
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 ] β ) . 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 ] β , 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 . |
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 . |
= = 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 / 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 . |
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 . |
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 . |
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 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 . |
= = Occurrence and production = = |
Xenon is a trace gas in Earth 's atmosphere , occurring at 87 Β± 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 . |
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 β 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 β 7 @,@ 000 m3 . Because of its low abundance , xenon is much more expensive than the lighter noble gases β approximate prices for the purchase of small quantities in Europe in 1999 were 10 β¬ / L for xenon , 1 β¬ / L for krypton , and 0 @.@ 20 β¬ / L for neon ; the much more plentiful argon costs less than a cent per liter . |
Within the Solar System , the nucleon fraction of xenon is 1 @.@ 56 Γ 10 β 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 β small , subplanetary bodies β 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 . |
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 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 Γ 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 . |
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 ) . |
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 β 2 and a nonzero quadrupole moment , and has t1 relaxation times in the millisecond and second ranges . |
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 Γ 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 . |
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 . |
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 . |
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 . |
= = 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 NiF |
2 catalyst yields XeF |
6 . Pyrolysis of XeF |
6 in the presence of NaF yields high @-@ purity XeF |
4 . |
The xenon fluorides behave as both fluoride acceptors and fluoride donors , forming salts that contain such cations as XeF + and Xe |
2F + |
3 , and anions such as XeF β |
5 , XeF β |
7 , and XeF2 β |
8 . The green , paramagnetic 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 dichloride , XeCl2 . Xenon dichloride is reported to be an endothermic , colorless , crystalline compound that decomposes into the elements at 80 Β° 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 |
2 is a real compound and not merely a van der Waals molecule consisting of weakly bound Xe atoms and Cl |
2 molecules . Theoretical calculations indicate that the linear molecule XeCl |
2 is less stable than the van der Waals complex . |
= = = Oxides and oxohalides = = = |
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