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21 décembre 2011 3 21 /12 /décembre /2011 02:28

Dietary intake

The daily Dietary Reference Intake recommended by the United States Institute of Medicine is between 110 and 130 µg for infants up to 12 months,Sony VAIO VPCF115FG/B Battery

90 µg for children up to eight years, 130 µg for children up to 13 years, 150 µg for adults, 220 µg for pregnant women and 290 µg for lactating mothers.[34] The Tolerable Upper Intake Level (UL) for adults is 1,100 ?g/day (1.1 mg/day).[35] The tolerable upper limit was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone.Sony VAIO VPCF116FGBI Battery

The thyroid gland needs no more than 70 micrograms /day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of body systems, including lactating breast, gastric mucosa, salivary glands, oral mucosa, thymus, epidermis, choroid plexus, etc.Sony VAIO VPCF117FJ/W Battery

The high iodide-concentration of thymus tissue in particular suggests an anatomical rationale for this role of iodine in the immune system.[39] The trophic, antioxidant and apoptosis-inductor actions and the presumed anti-tumour activity of iodides has been suggested to also be important for prevention of oral and salivary glands diseases.Sony VAIO VPCF117HG/BI Battery

Natural sources of iodine include sea life, such as kelp and certain seafood, as well as plants grown on iodine-rich soil. Iodized salt is fortified with iodine.

As of 2000, the median intake of iodine from food in the United States was 240 to 300 ?g/day for men and 190 to 210 ?g/day for women.Sony VAIO VPCF118FJ/W Battery

In Japan, consumption is much higher, owing to the frequent consumption of seaweed or kombu kelp.

After iodine fortification programs (e.g., iodized salt) have been implemented, some cases of iodine-induced hyperthyroidism have been observed (so called Jod-Basedow phenomenon). The condition seems to occur mainly in people over forty, and the risk appears higher when iodine deficiency is severe and the initial rise in iodine intake is high.Sony VAIO VPCF119FC Battery

It should also be noted that information processing, fine motor skills, and visual problem solving are improved by iodine repletion in moderately iodine-deficient children.

Deficiency

In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency gives rise to hypothyroidism, symptoms of which are extreme fatigue, goitre, mental slowing, depression, weight gain, and low basal body temperatures.Sony VAIO VPCF119FC/BI Battery

Iodine deficiency is the leading cause of preventable mental retardation, a result that occurs primarily when babies or small children are rendered hypothyroidic by a lack of the element. The addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but, as of March 2006, iodine deficiency remained a serious public health problem in the developing world.Sony VAIO VPCF119FJ/BI Battery

Iodine deficiency is also a problem in certain areas of Europe.

Other possible health effects being investigated as being related to deficiency include:

  • Breast cancer. The breast strongly and actively concentrates iodine into breast-milk for the benefit of the developing infant, and may develop a goiter-like hyperplasia, sometimes manifesting as fibrocystic breast disease, when iodine level are low.Sony VAIO VPCF11AFJ Battery
  • Studies indicate that iodine deficiency, either dietary or pharmacologic, can lead to breast atypia and increased incidence of malignancy in animal models, while iodine treatment can reverse dysplasia . The role of iodide in breast dysplasia and development of breast cancer is an area of active research.Sony VAIO VPCF11AGJ Battery
  • Stomach cancer. Some researchers have found an epidemiologic correlation between iodine deficiency, iodine-deficient goitre and gastric cancer. A decrease of the incidence of death rate from stomach cancer after implementation of the effective iodine-prophylaxis has been reported also.Sony VAIO VPCF11AHJ Battery

Precautions and toxicity of elemental iodine

Elemental iodine is an oxidizing irritant and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine and Lugol's solution are capable of causing tissue damage if use for cleaning and antisepsis is prolonged.Sony VAIO VPCF11JFX/B Battery

Elemental iodine (I2) is poisonous if taken orally in larger amounts; 2–3 grams of it is a lethal dose for an adult human.

Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m3 (eight-hour time-weighted average).Sony VAIO VPCF11M1E Battery

Toxicity of iodide ion

Excess iodine has symptoms similar to those of iodine deficiency. Commonly encountered symptoms are abnormal growth of the thyroid gland and disorders in functioning and growth of the organism as a whole. Iodides are similar in toxicity to bromides.Sony VAIO VPCF11M1E/H Battery

Excess iodine can be more cytotoxic in the presence of selenium deficiency. Iodine supplementation in selenium-deficient populations is, in theory, problematic, partly for this reason.

Iodine sensitivity

Some people develop a sensitivity to iodine. Application of tincture of iodine can cause a rash. Some cases of reaction to Povidone-iodine (Betadine) have been documented to be a chemical burn.Sony VAIO VPCF11MFX/B Battery

Eating iodine-containing foods can cause hives. Medical use of iodine (i.e. as a contrast agent, see above) can causeanaphylactic shock in highly iodine-sensitive patients. Some cases of sensitivity to iodine can be formally classified as iodine allergies. Iodine sensitivity is rare but has a considerable effect given the extremely widespread use of iodine-based contrast media.Sony VAIO VPCF11S1E Battery

Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced  A colorless, heavy, odorless noble gas, xenon 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.Sony VAIO VPCF11S1E/B Battery

Naturally occurring xenon consists of nine 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 from iodine-135 as a result ofnuclear fission, and it acts as the most significant neutron absorber in nuclear reactors.Sony VAIO VPCF11Z1E Battery

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.Sony VAIO VPCF11Z1E/BI Battery

Xenon was discovered in England by William Ramsay and Morris Travers on July 12, 1898, shortly after their discovery of the elements krypton and neon. They found it in the residue left over from evaporating components of liquid air. Ramsay suggested the name xenon for this gas from theGreek word ????? [xenon], neuter singular form of ????? [xenos], meaning 'foreign(er)', 'strange(r)', or 'guest'.Sony VAIO VPCF11ZHJ Battery

In 1902, Ramsay estimated the proportion of xenon in the Earth's atmosphere as one part in 20 million.

During the 1930s, 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 electrical current through a tube filled with xenon gas. In 1934, Edgerton was able to generate flashes as brief as one microsecond with this method.Sony VAIO VPCF127HGBI Battery

In 1939, 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 ananesthetic.Sony VAIO VPCF137HG/BI Battery

Although Lazharev, in Russia, apparently studied xenon anesthesia in 1941, the first published report confirming xenon anesthesia was in 1946 by J. H. Lawrence, who experimented on mice. Xenon was first used as a surgical anesthetic in 1951 by Stuart C. Cullen, who successfully operated on two patients.Sony VAIO VPCS111FM/S Battery

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]–).Sony VAIO VPCS115EC Battery

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.Sony VAIO VPCS115FG Battery

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.Sony VAIO VPCS117GG Battery

Characteristics

Xenon has atomic number 54; that is, its nucleus contains 54 protons. Atstandard 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.Sony VAIO VPCS117GGB Battery

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.Sony VAIO VPCS118EC Battery

It is completely metallic at 155 GPa. When metalized, 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.

Xenon is a member of the zero-valence elements that are called noble or inert gases.Sony VAIO VPCS119FJ/B Battery

It is inert to most common chemical reactions (such as combustion, for example) because the outer valence shellcontains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. However, xenon can be oxidized by powerful oxidizing agents, and many xenon compounds have been synthesized.Sony VAIO VPCS119GC Battery

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,[45] but the most intense lines occur in the region of blue light, which produces the coloration.Sony VAIO VPCS11AFJ Battery

Occurrence and production

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,[47]and is also found in gases emitted from some mineral springs.

Xenon is obtained commercially as a byproduct of the separation of air into oxygen and nitrogen.Sony VAIO VPCS11AGJ Battery

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 adsorption onto silica gel or by distillation.Sony VAIO VPCS11AHJ Battery

Finally, the krypton/xenon mixture may be separated into krypton and xenon via distillation.  Extraction of a liter of xenon from the atmosphere requires 220 watt-hours of energy.[50] Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3.Sony VAIO VPCS11AVJ Battery

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.

Within the Solar System, the nucleon fraction of xenon is 1.56 × 10?8, for an abundance of one part in 64 million of the total mass.Sony VAIO VPCS11J7E/B Battery

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.Sony VAIO VPCS11M1E/W Battery

(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.Sony VAIO VPCS11V9E Battery

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.Sony VAIO VPCS11V9E/B Battery

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 classicalnovae explosions and from the radioactive decay of elements such as iodine, uranium and plutonium.Sony VAIO VPCS11X9E/B Battery

Isotopes and isotopic studies

Naturally occurring xenon is made of nine 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, 134Xe and 136Xe are predicted to undergo double beta decay, but this has never been observed so they are considered to be stable.Sony VAIO VPCS123FGB Battery

Besides these stable forms, there are over 40 unstable isotopes that have been studied. 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.Sony VAIO VPCS125EC Battery

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.Sony VAIO VPCS128EC Battery

The resulting spin polarization of xenon nuclei can surpass 50% of its maximum possible value, greatly exceeding the equilibrium value dictated by the Boltzmann distribution (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.Sony VAIO VPCS129GC Battery

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,Sony VAIO VPCS12C7E/B Battery

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.Sony VAIO VPCS12L9E/B Battery

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.

Some radioactive isotopes of xenon, for example, 133Xe and 135Xe, are produced by neutron irradiation of fissionable material within nuclear reactors.Sony VAIO VPCS12V9E/B Battery

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 aneutron 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.Sony VAIO VPCY115FGS Battery

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).[69] 135Xe reactor poisoning played a major role in the Chernobyl disaster.[70] A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit.Sony VAIO VPCY115FX/BI Battery

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.Sony VAIO VPCY115FXBI Battery

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.Sony VAIO VPCY118EC Battery

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.Sony VAIO VPCY118GX/BI Battery

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.Sony VAIO VPCY119FJ/S Battery

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.Sony VAIO VPCY11AFJ Battery

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 fromNew Mexico was believed to be from the decay of mantle-derived gases soon after Earth's formation.Sony VAIO VPCY11AGJ Battery

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.Sony VAIO VPCY11AHJ Battery

Halides

Three fluorides are known: XeF2, XeF4, and XeF6. The fluorides are the starting point for the synthesis of almost all xenon compounds.

The solid, crystalline difluoride XeF2 is formed when a mixture of fluorine and xenon gases is exposed to ultraviolet light.Sony VAIO VPCY11AVJ Battery

Ordinary daylight is sufficient.Long-term heating of XeF2 at high temperatures under an NiF2 catalyst yields XeF6.[82]Pyrolysis of XeF6 in the presence of NaF yields high-purity XeF4.

The xenon fluorides behave as both fluoride acceptors and fluoride donors, forming salts that contain such cations as XeF+ and Xe2F3+, and anions such as XeF5?, XeF7?, and XeF82?.Sony VAIO VPCY11M1E/S Battery

The green, paramagnetic Xe2+ is formed by the reduction of XeF2 by xenon gas.

XeF2 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.Sony VAIO VPCY11S1E Battery

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 XeCl2 is a real compound and not merely a van der Waals molecule consisting of weakly bound Xe atoms and Cl2 molecules.Sony VAIO VPCY11V9E/S Battery

Theoretical calculations indicate that the linear molecule XeCl2 is less stable than the van der Waals complex.

Oxides and oxohalides

Three oxides of xenon are known: xenon trioxide (XeO3) and xenon tetroxide (XeO4), both of which are dangerously explosive and powerful oxidizing agents. Xenon dioxide (XeO2) was reported in 2011 with a coordination number of four.Sony VAIO VPCY218EC/BI Battery

XeO2 forms when xenon fluoride is poured over ice. Its crystal structure may allow it to replace silicon in silicate minerals. XeOO+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 XeF6:Sony VAIO VPCY218EC/G Battery

XeF6 + 3 H2O ? XeO3 + 6 HF

XeO3 is weakly acidic, dissolving in alkali to form unstable xenate salts containing the HXeO?
4 anion. These unstable salts easilydisproportionate into xenon gas and perxenate salts, containing the XeO4?
6 anion.[91]

Barium perxenate, when treated with concentrated sulfuric acid, yields gaseous xenon tetroxide:Sony VAIO VPCY218EC/L Battery

Ba2XeO6 + 2 H2SO4 ? 2 BaSO4 + 2 H2O + XeO4

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 oxyfluorides are known, including XeOF2, XeOF4, XeO2F2, and XeO3F2. XeOF2 is formed by the reaction of OF2with xenon gas at low temperatures.Sony VAIO VPCY218EC/P Battery

It may also be obtained by the partial hydrolysis of XeF4. It disproportionates at ?20 °C into XeF2 and XeO2F2. XeOF4 is formed by the partial hydrolysis ofXeF6,[93] or the reaction of XeF6 with sodium perxenate, Na4XeO6. The latter reaction also produces a small amount of XeO3F2.Sony VAIO VPCY21S1E/L Battery

XeOF4 reacts with CsF to form the XeOF?5anion, while XeOF3 reacts with the alkali metal fluorides KF, RbF and CsF 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, particularlycarbon.Sony VAIO VPCY21S1E/P Battery

Electron-withdrawing groups, such as groups with fluorine substitution, are necessary to stabilize these compounds.[91] Numerous such compounds have been characterized, including:

  • C6F5–Xe+–N?C–CH3, where C6F5 is the pentafluorophenyl group.
  • [C6F5]2Xe
  • C6F5–Xe–X, where X is CN, F, or Cl.
  • R–C?C–Xe+, where R is C2F?
    5 or tert-butyl.
  • C6F5–XeF+
    2
  • (C6F5Xe)2Cl+

Other compounds containing xenon bonded to a less electronegative element include F–Xe–N(SO2F)2 and F–Xe–BF2. The latter is synthesized from dioxygenyltetrafluoroborate, O2BF4, at ?100 °C.Sony VAIO VPCY21S1E/SI Battery

An unusual ion containing xenon is the tetraxenonogold(II) cation, AuXe2+

4, which contains Xe–Au bonds.[99] This ion occurs in the compound AuXe4(Sb2F11)2, and is remarkable in having direct chemical bonds between two notoriously unreactive atoms, xenon and gold, with xenon acting as a transition metal ligand.Sony VAIO VPCCW2S5C CN1 Battery

In 1995, M. Räsänen and co-workers, scientists at the University of Helsinki in Finland, announced the preparation of xenon dihydride (HXeH), and later xenon hydride-hydroxide (HXeOH), hydroxenoacetylene (HXeCCH), and other Xe-containing molecules.Sony VAIO VPCEA20 Battery

In 2008, Khriachtchev et al. reported the preparation of HXeOXeH by the photolysis of water within a cryogenic xenon matrix. Deuterated molecules, HXeOD and DXeOH, have also been produced.

Clathrates and excimers

In addition to compounds where xenon forms a chemical bond, xenon can form clathrates—substances where xenon atoms are trapped by the crystalline lattice of another compound.Sony VAIO VPCEB10 Battery

An example is xenon hydrate (Xe·5.75 H2O), where xenon atoms occupy vacancies in a lattice of water molecules. This clathrate has a melting point of 24 °C.The deuterated version of this hydrate has also been produced. Such clathrate hydrates can occur naturally under conditions of high pressure, such as in Lake Vostok underneath the Antarctic ice sheet.Sony VAIO VPCEB11FM Battery

Clathrate formation can be used to fractionally distill xenon, argon and krypton.

Xenon can also form endohedral 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.Sony VAIO VPCEB11FM/BI Battery

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.

While xenon atoms are at their ground energy state, they repel each other and will not form a bond.Sony VAIO VPCEB11FM/T Battery

When xenon atoms becomes energized, however, they can form anexcimer (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.Sony VAIO VPCEB11FM/WI Battery

The typical lifetime of a xenon excimer is 1–5 ns, and the decay releases photons withwavelengths of about 150 and 173 nm. Xenon can also form excimers with other elements, such as the halogens bromine, chlorine and fluorine.

Applications

Although xenon is rare and relatively expensive to extract from the Earth's atmosphere, it has a number of applications.Sony VAIO VPCEB11FX Battery

Gas-discharge lamps

Xenon is used in light-emitting devices called xenon flash lamps, which are used in photographic flashes and stroboscopic lamps; to excite the active medium inlasers which then generate coherent light; and, occasionally, in bactericidal lamps. The first solid-state laser, invented in 1960, was pumped by a xenon flash lamp, and lasers used to power inertial confinement fusion are also pumped by xenon flash lamps.Sony VAIO VPCEB11FX/BI Battery

Continuous, short-arc, high pressure xenon arc lamps have a color temperature closely approximating noon sunlight and are used insolar simulators. That is, the chromaticity of these lamps closely approximates a heated black body radiator that has a temperature close to that observed from the Sun.Sony VAIO VPCEB11FX/T Battery

After they were first introduced during the 1940s, these lamps began replacing the shorter-lived carbon arc lamps in movie projectors.[13] They are employed in typical 35mm and IMAX film projection systems, automotive HID headlights, high-end "tactical" flashlights and other specialized uses.Sony VAIO VPCEB11FX/WI Battery

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 visionsystems.

The individual cells in a plasma display use a mixture of xenon and neon that is converted into a plasma using electrodes.Sony VAIO VPCEB11GX Battery

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 conductivity and lowest ionization potential of all the non-radioactive noble gases.Sony VAIO VPCEB11GX/BI Battery

As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp. The low thermal conductivity minimizes 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.Sony VAIO VPCEB11GX/T Battery

Lasers

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 lasing medium. The first excimer laser used a xenon dimer (Xe2) energized by a beam of electrons to produce stimulated emission at an ultraviolet wavelength of 176 nm.Sony VAIO VPCEB11GX/WI Battery

Xenon chloride and xenon fluoride have also been used in excimer (or, more accurately, exciplex) lasers. The xenon chloride excimer laser has been employed, for example, in certain dermatological uses.

Anesthesia

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.Sony VAIO VPCEB12FX Battery

Two physiological mechanisms for xenon anesthesia have been proposed. The first one involves the inhibition of the calcium ATPase pump—the mechanism cells use to remove calcium (Ca2+)—in the cell membrane of synapses. This results from a conformational change when xenon binds to nonpolar sites inside the protein.Sony VAIO VPCEB12FX/BI Battery

The second mechanism focuses on the non-specific interactions between the anesthetic and the lipid membrane.

Xenon has a minimum alveolar concentration (MAC) of 72% at age 40, making it 44% more potent than N2O as an anesthetic. Thus it can be used in concentrations with oxygen that have a lower risk of hypoxia.Sony VAIO VPCEB12FX/BIC Battery

Unlike nitrous oxide (N2O), xenon is not a greenhouse 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.

Neuroprotectant

Xenon is finding application in treating brain injuries, since it is an antagonist of N-methyl-d-aspartate receptors (NMDA receptors).Sony VAIO VPCEB12FX/T Battery

These receptors exacerbate the damage from oxygen deprivation and xenon performs better as a neuroprotectant than either ketamine or nitrous oxide, which have undesired side-effects. 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 authorisation of clinical trials for similar cases.Sony VAIO VPCEB14FX Battery

The treatment is done simultaneously with cooling the body temperature to 33.5 °C.

Imaging

Gamma emission from the radioisotope 133Xe of xenon can be used to image the heart, lungs, and brain, for example, by means of single photon emission computed tomography. 133Xe has also been used to measure blood flow.Sony VAIO VPCEB14FX/BI Battery

Xenon, particularly hyperpolarized 129Xe, is a useful contrast agent for magnetic resonance imaging (MRI). In the gas phase, it can be used to image empty space such as cavities in a porous sample or alveoli in lungs. Hyperpolarization renders 129Xe much more detectable via magnetic resonance imaging and has been used for studies of the lungs and other tissues.Sony VAIO VPCEB14FX/T Battery

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 solvents, it can be used to image various soft living tissues.

NMR spectroscopy

Because of the 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 the xenon atom.Sony VAIO VPCEB14FX/WI Battery

For instance xenon dissolved in water, xenon dissolved in hydrophobic solvent, and xenon associated with certain proteins can be distinguished by NMR.

Hyperpolarized xenon can be used by surface-chemists. Normally, it is difficult to characterize surfaces using NMR,Sony VAIO VPCEB15FM Battery

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, bytransferrering spin polarization to them from hyperpolarized xenon gas. This makes the surface signals strong enough to measure, and distinguishes them from bulk signals.Sony VAIO VPCEB15FM/BI Battery

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 nucleartest ban treaties, as well as to confirm nuclear test explosions by states such as North Korea.Sony VAIO VPCEB15FM/T Battery

Liquid xenon is being used in calorimeters for measurements of gamma rays as well as a medium for detecting hypotheticalweakly interacting massive particles, or WIMPs. When a WIMP collides with a xenon nucleus, it should, theoretically, strip an electron and create a primary scintillation.Sony VAIO VPCEB15FM/WI Battery

By using xenon, this burst of energy could then be readily distinguished from similar events caused by particles such as cosmic rays. However, the XENON experiment at the Gran Sasso National Laboratory in Italy and the ZEPLIN-II and ZEPLIN-III experiments at the Boulby Underground Laboratory in the UK have thus far failed to find any confirmed WIMPs.Sony VAIO VPCEB15FX Battery

Even if no WIMPs are detected, the experiments will serve to constrain the properties of dark matter and some physics models. The current detector at the Gran Sasso facility has demonstrated sensitivity comparable to that of the best cryogenic detectors, and the sensitivity was expected to be increased by an order of magnitude in 2009.Sony VAIO VPCEB15FX/BI Battery

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.Sony VAIO VPCEB15FX/T Battery

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 Europe's SMART-1 spacecraft and for the three ion propulsion engines on NASA's Dawn Spacecraft.Sony VAIO VPCEB15FX/WI Battery

Chemically, the perxenate compounds are used as oxidizing agents in analytical chemistry. Xenon difluoride is used as an etchant for silicon, particularly in the production of microelectromechanical systems (MEMS). The anticancer drug 5-fluorouracil can be produced by reacting xenon difluoride with uracil.Sony VAIO VPCEB16FX Battery

Xenon is also used in protein crystallography. Applied at pressures from 0.5 to 5 MPa (5 to 50 atm) to a protein crystal, xenon atoms bind in predominantly hydrophobic cavities, often creating a high quality, isomorphous, heavy-atom derivative, which can be used for solving the phase problem.Sony VAIO VPCEB16FX/B Battery

Precautions

Many oxygen-containing xenon compounds are toxic due to their strong oxidative properties, and explosive due to their tendency to break down into elemental xenon plus diatomic oxygen (O2), which contains much stronger chemical bonds than the xenon compounds.Sony VAIO VPCEB16FX/G Battery

Xenon gas can be safely kept in normal sealed glass or metal containers at standard temperature and pressure. However, it readily dissolves in most plastics 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.Sony VAIO VPCEB16FX/L Battery

At 169 m/s, the speed of sound in xenon gas is slower than that in air due to the slower average speed of the heavy xenon atoms compared to nitrogen and oxygen molecules. Hence, xenon lowers the resonant frequencies of the vocal tract when inhaled. This produces a characteristic lowered voice timbre, an effect opposite to the high-timbred voice caused by inhalation of helium.Sony VAIO VPCEB16FX/P Battery

Like helium, xenon does not satisfy the body's need for oxygen. Xenon is both a simple asphyxiant 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 asphyxiant without being anesthetic.Sony VAIO VPCEB16FX/W Battery

It is possible to safely breathe heavy gases such as xenon or sulfur hexafluoride when they are in a mixture with oxygen; the oxygen comprising at least 20% of the mixture. Xenon at 80% concentration along with 20% oxygen rapidly produces the unconsciousness of general anesthesia (and has been used for this, as discussed above).Sony VAIO VPCEB17FX Battery

Breathing 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 invisibly in a container, and if a person enters a container filled with an odorless, colorless gas, they may find themselves breathing it unknowingly. Sony VAIO VPCEB17FX/B Battery

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 unventilated space.Sony VAIO VPCEB17FX/G Battery,Sony VAIO VPCEB17FX/L Battery,Sony VAIO VPCEB17FX/P Battery,Sony VAIO VPCEB17FX/W Battery,Sony VAIO VPCEB190X Battery,Sony VAIO VPCEB19FX Battery,Sony VAIO VPCEB19GX Battery

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