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= Xenon =
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Introduction
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Xenon is a chemical element; it has symbol Xe and atomic number 54. It
is a dense, colorless, odorless noble gas found in Earth's atmosphere
in trace amounts. Although generally unreactive, it 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 the lasing medium, and the earliest laser designs used xenon
flash lamps as pumps. Xenon is also used to search for hypothetical
weakly interacting massive particles and as a propellant for ion
thrusters in spacecraft.
Naturally occurring xenon consists of seven stable isotopes and two
long-lived radioactive isotopes. More than 40 unstable xenon isotopes
undergo radioactive decay, and 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 (a
product of nuclear fission), and is the most significant (and
unwanted) neutron absorber in nuclear reactors.
History
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Xenon was discovered in England by the Scottish chemist William Ramsay
and English chemist Morris Travers on July 12, 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 'xénon', neuter singular form of ξένος 'xénos', meaning
'foreign(er)', 'strange(r)', or 'guest'. In 1902, Ramsay estimated the
proportion of xenon in the Earth's atmosphere to be 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
passing 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 used it with 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 (). Since O2 (1165 kJ/mol) and xenon (1170 kJ/mol)
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]−, but later work
revealed that it was probably a mixture of various xenon-containing
salts. Since then, many other xenon compounds have been discovered, in
addition to 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 1989, 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 initialism. It was the first-time atoms had been
precisely positioned on a flat surface.
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
5.894 kg/m3, about 4.5 times the density of the Earth's atmosphere at
sea level, 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.
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 greater than the average
density of granite, 2.75 g/cm3. Under gigapascals of pressure, xenon
forms 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 appears
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 width of the electron bands in that state.
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
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, producing the coloration.
Occurrence and production
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Xenon is a trace gas in Earth's atmosphere, occurring at a volume
fraction of (parts per billion), or approximately 1 part per 11.5
million. It is also found as a component of gases emitted from some
mineral springs. Given a total mass of the atmosphere of 5.15e18 kg,
the atmosphere contains on the order of 2.03 Gt of xenon in total when
taking the average molar mass of the atmosphere as 28.96 g/mol which
is equivalent to some 394-mass ppb.
The missing Xe problem
========================
The concentration of Xe in the atmosphere is much lower than Ar and
Kr, a geological mystery known as "the missing Xe problem". Numerous
proposals have been made to explain the mystery, including formation
of Xe-Fe oxides in the Earth's lower mantle, formation xenon dioxide
in silica, and reactions between Xe and Fe/Ni in the Earth's core.
Commercial
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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, the liquid oxygen may be
enriched to contain 0.1-0.2% of a krypton/xenon mixture, which is
extracted either by adsorption onto silica gel or by distillation.
Finally, the krypton/xenon mixture may be separated into krypton and
xenon by further distillation.
Worldwide production of xenon in 1998 was estimated at 5,000-7,000 m3.
At a density of this is equivalent to roughly . Because of its
scarcity, 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 (=~€1.7/g) for xenon, 1 €/L (=~€0.27/g) for
krypton, and 0.20 €/L (=~€0.22/g) for neon, while the much more
plentiful argon, which makes up over 1% by volume of earth's
atmosphere, costs less than a cent per liter.
Solar System
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Within the Solar System, the nucleon fraction of xenon is , 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 abundance of xenon in the atmosphere of
planet Jupiter is unusually high, about 2.6 times that of the Sun.
This abundance remains unexplained, but may have been caused by an
early and rapid buildup of planetesimals--small, sub-planetary
bodies--before the heating of the presolar disk; otherwise, xenon
would not have been trapped in the planetesimal ices. The problem of
the low terrestrial xenon may be explained by covalent bonding of
xenon to oxygen within quartz, reducing the outgassing of xenon into
the atmosphere.
Stellar
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Unlike the lower-mass noble gases, the normal stellar nucleosynthesis
process inside a star does not form xenon. Nucleosynthesis consumes
energy to produce nuclides more massive than iron-56, and thus the
synthesis of xenon represents no energy gain for a star. Instead,
xenon is formed during supernova explosions during the r-process, by
the slow neutron-capture process (s-process) in red giant stars that
have exhausted their core hydrogen and entered the asymptotic giant
branch, and from radioactive decay, for example by beta decay of
extinct iodine-129 and spontaneous fission of thorium, uranium, and
plutonium.
Nuclear fission
=================
Xenon-135 is a notable neutron poison with a high fission product
yield. As it is relatively short lived, it decays at the same rate it
is produced during 'steady' operation of a nuclear reactor. However,
if power is reduced or the reactor is scrammed, less xenon is
destroyed than is produced from the beta decay of its parent nuclides.
This phenomenon called xenon poisoning can cause significant problems
in restarting a reactor after a scram or increasing power after it had
been reduced and it was one of several contributing factors in the
Chernobyl nuclear accident.
Stable or extremely long lived isotopes of xenon are also produced in
appreciable quantities in nuclear fission. Xenon-136 is produced both
as a fission product and when xenon-135 undergoes neutron capture
before it can decay. The ratio of xenon-136 to xenon-135 (or its decay
products) can give hints as to the power history of a given reactor or
identify a nuclear explosion, as xenon-135 is mostly produced by
successive beta decays of more neutron-rich fission products. These
short-lived nuclides do not share its neutron-absorbing prowess, and
so absorb fewer neutrons during the brief moment of a nuclear
explosion, lowering the ratio of mass-136 to mass-135 products.
The stable isotope xenon-132 has a fission product yield of over 4% in
the thermal neutron fission of which means that stable or nearly
stable xenon isotopes have a higher mass fraction in spent nuclear
fuel (which is about 3% fission products) than it does in air.
However, there is as of 2022 no commercial effort to extract xenon
from spent fuel during nuclear reprocessing.
Isotopes
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Naturally occurring xenon is composed of seven stable and two almost
stable isotopes: 126Xe, 128-132Xe, and 134Xe are stable, 124Xe and
136Xe have very long half-lives, trillions of times the age of the
universe. The isotopes 126Xe and 134Xe are predicted by theory to
undergo double beta decay, but this has never been observed so they
are considered stable. More than 40 unstable isotopes are known. The
longest-lived of these isotopes are the primordial 124Xe, which
undergoes double electron capture with a half-life of , and 136Xe,
which undergoes double beta decay with a half-life of . 129Xe is
produced by beta decay of 129I, which has a half-life of 16 million
years. 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission
products of 235U and 239Pu, and are used to detect and monitor nuclear
explosions.
Nuclear spin
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Nuclei of two of the stable isotopes of xenon, 129Xe and 131Xe (both
stable isotopes with odd mass numbers), 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 the
hyperpolarization persists for long periods even after the engendering
light and vapor have been removed. 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 and a nonzero
quadrupole moment, and has t1 relaxation times in the millisecond and
second ranges.
From fission
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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 million barns, and operates 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. However,
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 was a major factor in the Chernobyl disaster.
A shutdown or decrease of power of a reactor can result in buildup of
135Xe, with reactor operation going into a condition known as the
iodine pit. Under adverse conditions, relatively high concentrations
of radioactive xenon isotopes may emanate from cracked fuel rods, or
fissioning of uranium in cooling water.
Isotope ratios of xenon produced in natural nuclear fission reactors
at Oklo in Gabon reveal the reactor properties during chain reaction
that took place about 2 billion years ago.
Cosmic processes
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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.
Because the half-life of 129I is comparatively short on a cosmological
time scale (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, because the 129I isotope was likely
generated shortly before the Solar System was formed, seeding 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 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) but Mars shows a greater abundance of 129Xe than the Earth or
the Sun. Since 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 is believed to be from the decay of
mantle-derived gases from soon after Earth's formation.
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. The chemistry of xenon in
each oxidation state is analogous to that of the neighboring element
iodine in the immediately lower oxidation state.
Halides
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Three fluorides are known: xenon difluoride, xenon tetrafluoride, and
xenon hexafluoride. XeF is theorized to be unstable. These are the
starting points for the synthesis of almost all xenon compounds.
The solid, crystalline difluoride is formed when a mixture of
fluorine and xenon gases is exposed to ultraviolet light. The
ultraviolet component of ordinary daylight is sufficient. Long-term
heating of at high temperatures under an catalyst yields . Pyrolysis
of in the presence of NaF yields high-purity .
The xenon fluorides behave as both fluoride acceptors and fluoride
donors, forming salts that contain such cations as and , and anions
such as , , and . The green, paramagnetic is formed by the reduction
of by xenon gas.
also forms coordination complexes with transition metal ions. More
than 30 such complexes have been synthesized and characterized.
Whereas the xenon fluorides are well characterized, the other halides
are not. Xenon dichloride, formed by the high-frequency irradiation
of a mixture of xenon, fluorine, and silicon or carbon tetrachloride,
is reported to be an endothermic, colorless, crystalline compound that
decomposes into the elements at 80 °C. However, may be merely a van
der Waals molecule of weakly bound Xe atoms and molecules and not a
real compound. Theoretical calculations indicate that the linear
molecule is less stable than the van der Waals complex. Xenon
tetrachloride and xenon dibromide are even more unstable and they
cannot be synthesized by chemical reactions. They were created by
radioactive decay of and , respectively.
Oxides and oxohalides
=======================
Three oxides of xenon are known: xenon trioxide () and xenon tetroxide
(), 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.
Xenon does not react with oxygen directly; the trioxide is formed by
the hydrolysis of :
: + 3 → + 6 HF
is weakly acidic, dissolving in alkali to form unstable 'xenate'
salts containing the anion. These unstable salts easily
disproportionate into xenon gas and perxenate salts, containing the
anion.
Barium perxenate, when treated with concentrated sulfuric acid, yields
gaseous xenon tetroxide:
: + 2 → 2 + 2 +
To prevent decomposition, the xenon tetroxide thus formed is quickly
cooled into a pale-yellow solid. It explodes above −35.9 °C into xenon
and oxygen gas, but is otherwise stable.
A number of xenon oxyfluorides are known, including , xenon
oxytetrafluoride, , and . is formed by reacting oxygen difluoride
with xenon gas at low temperatures. It may also be obtained by partial
hydrolysis of . It disproportionates at −20 °C into and . is formed
by the partial hydrolysis of ...
: + → + 2
...or the reaction of with sodium perxenate, . The latter reaction
also produces a small amount of .
is also formed by partial hydrolysis of .
: + 2 → + 4
reacts with CsF to form the anion, while XeOF3 reacts with the
alkali metal fluorides KF, RbF and CsF to form the anion.
Other compounds
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Xenon can be directly bonded to a less electronegative element than
fluorine or oxygen, particularly carbon. Electron-withdrawing groups,
such as groups with fluorine substitution, are necessary to stabilize
these compounds. Numerous such compounds have been characterized,
including:
* , where C6F5 is the pentafluorophenyl group.
*
*
*
*
*
*
*
*
Other compounds containing xenon bonded to a less electronegative
element include and . The latter is synthesized from dioxygenyl
tetrafluoroborate, , at −100 °C.
An unusual ion containing xenon is the tetraxenonogold(II) cation, ,
which contains Xe-Au bonds. This ion occurs in the compound , and is
remarkable in having direct chemical bonds between two notoriously
unreactive atoms, xenon and gold, with xenon acting as a transition
metal ligand. A similar mercury complex (HgXe)(Sb3F17) (formulated as
[HgXe2+][Sb2F11-][SbF6-]) is also known.
The compound contains a Xe-Xe bond, the longest element-element bond
known (308.71 pm = 3.0871 Å).
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. 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 or pairs are trapped by
the crystalline lattice of another compound. One example is xenon
hydrate (Xe·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. Another
example is xenon hydride (Xe(H2)8), in which xenon pairs (dimers) are
trapped inside solid hydrogen. Such clathrate hydrates can occur
naturally under conditions of high pressure, such as in Lake Vostok
underneath the Antarctic ice sheet. 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 observed by 129Xe nuclear magnetic resonance (NMR)
spectroscopy. Through the sensitive chemical shift of the xenon atom
to its environment, chemical reactions on the fullerene molecule can
be analyzed. These observations are not without caveat, however,
because the xenon atom has an electronic influence on the reactivity
of the fullerene.
When xenon atoms are in the ground energy state, they repel each other
and will not form a bond. When xenon atoms becomes energized, however,
they can form an excimer (excited dimer) until the electrons return to
the ground state. This entity is formed because the xenon atom tends
to complete the outermost electronic shell by adding an electron from
a neighboring xenon atom. The typical lifetime of a xenon excimer is
1-5 nanoseconds, and the decay releases photons with wavelengths of
about 150 and 173 nm. Xenon can also form excimers with other
elements, such as the halogens bromine, chlorine, and fluorine.
Applications
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Although xenon is rare and relatively expensive to extract from the
Earth's atmosphere, it has a number of applications.
Gas-discharge lamps
=====================
Xenon is used in light-emitting devices called xenon flash lamps, used
in photographic flashes and stroboscopic lamps; to excite the active
medium in lasers 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.
Continuous, short-arc, high pressure xenon arc lamps have a color
temperature closely approximating noon sunlight and are used in solar
simulators. That is, the chromaticity of these lamps closely
approximates a heated black body radiator at the temperature of the
Sun. First introduced in the 1940s, these lamps replaced the
shorter-lived carbon arc lamps in movie projectors. They are also
employed in typical 35mm, IMAX, and digital film projection systems.
They are an excellent source of short wavelength ultraviolet radiation
and have intense emissions in the near infrared used in some night
vision systems. Xenon is used as a starter gas in metal halide lamps
for automotive HID headlights, and high-end "tactical" flashlights.
The individual cells in a plasma display contain a mixture of xenon
and neon ionized with electrodes. The interaction of this plasma with
the electrodes generates ultraviolet photons, which then excite the
phosphor coating on the front of the display.
Xenon is used as a "starter gas" in high pressure sodium lamps. It has
the lowest thermal conductivity and lowest ionization potential of all
the non-radioactive noble gases. As a noble gas, it does not interfere
with the chemical reactions occurring in the operating lamp. The low
thermal 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.
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.
Xenon chloride and xenon fluoride have also been used in excimer (or,
more accurately, exciplex) lasers.
Anesthesia
============
Xenon has been used as a general anesthetic, but it is more expensive
than conventional anesthetics.
Xenon interacts with many different receptors and ion channels, and
like many theoretically multi-modal inhalation anesthetics, these
interactions are likely complementary. Xenon is a high-affinity
glycine-site NMDA receptor antagonist. However, xenon is different
from certain other NMDA receptor antagonists in that it is not
neurotoxic and it inhibits the neurotoxicity of ketamine and nitrous
oxide (N2O), while actually producing neuroprotective effects. Unlike
ketamine and nitrous oxide, xenon does not stimulate a dopamine efflux
in the nucleus accumbens.
Like nitrous oxide and cyclopropane, xenon activates the two-pore
domain potassium channel TREK-1. A related channel TASK-3 also
implicated in the actions of inhalation anesthetics is insensitive to
xenon. Xenon inhibits nicotinic acetylcholine α4β2 receptors which
contribute to spinally mediated analgesia. Xenon is an effective
inhibitor of plasma membrane Ca2+ ATPase. Xenon inhibits Ca2+ ATPase
by binding to a hydrophobic pore within the enzyme and preventing the
enzyme from assuming active conformations.
Xenon is a competitive inhibitor of the serotonin 5-HT3 receptor.
While neither anesthetic nor antinociceptive, this reduces
anesthesia-emergent nausea and vomiting.
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 with oxygen in concentrations that have a lower risk of hypoxia.
Unlike nitrous oxide, xenon is not a greenhouse gas and is viewed as
environmentally friendly. Though recycled in modern systems, xenon
vented to the atmosphere is only returning to its original source,
without environmental impact.
Neuroprotectant
=================
Xenon induces robust cardioprotection and neuroprotection through a
variety of mechanisms. Through its influence on Ca2+, K+, KATP\HIF,
and NMDA antagonism, xenon is neuroprotective when administered
before, during and after ischemic insults. Xenon is a high affinity
antagonist at the NMDA receptor glycine site. Xenon is
cardioprotective in ischemia-reperfusion conditions by inducing
pharmacologic non-ischemic preconditioning. Xenon is cardioprotective
by activating PKC-epsilon and downstream p38-MAPK. Xenon mimics
neuronal ischemic preconditioning by activating ATP sensitive
potassium channels. Xenon allosterically reduces ATP mediated channel
activation inhibition independently of the sulfonylurea receptor1
subunit, increasing KATP open-channel time and frequency.
Sports doping and mountaineering
==================================
Inhaling a xenon/oxygen mixture activates production of the
transcription factor HIF-1-alpha, which may lead to increased
production of erythropoietin. The latter hormone is known to increase
red blood cell production and athletic performance. Reportedly, doping
with xenon inhalation has been used in Russia since 2004 and perhaps
earlier. On August 31, 2014, the World Anti Doping Agency (WADA) added
xenon (and argon) to the list of prohibited substances and methods,
although no reliable doping tests for these gases have yet been
developed. In addition, effects of xenon on erythropoietin production
in humans have not been demonstrated, so far.
In 2025, four UK mountaineers, including Alistair Carns, climbed Mount
Everest in an expedition lasting only one week, claiming their
inhalation of xenon gas to stimulate erythropoietin production had
obviated the usual several weeks' altitude acclimatisation. The
International Climbing and Mountaineering Federation (UIAA) criticised
the decision, citing that there is no evidence that the inhalation of
xenon improves performance in high elevation environments.
Furthermore, the UIAA warned that as an anesthetic, xenon gas could
result in impaired brain function, respiratory compromise, and death
if used in an unmonitored setting.
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.
Xenon, particularly hyperpolarized 129Xe, is a useful contrast agent
for magnetic resonance imaging (MRI). In the gas phase, it can image
cavities in a porous sample, alveoli in lungs, or the flow of gases
within the lungs. Because xenon is soluble both in water and in
hydrophobic solvents, it can image various soft living tissues.
Xenon-129 is used as a visualization agent in MRI scans. When a
patient inhales hyperpolarized xenon-129 ventilation and gas exchange
in the lungs can be imaged and quantified. Unlike xenon-133, xenon-129
is non-ionizing and is safe to be inhaled with no adverse effects.
Surgery
=========
The xenon chloride excimer laser has certain dermatological uses.
NMR spectroscopy
==================
Because of the xenon atom's large, flexible outer electron shell, the
NMR spectrum changes in response to surrounding conditions and can be
used to monitor the surrounding chemical circumstances. 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 with NMR because signals from a
surface are overwhelmed by signals from the atomic nuclei in the bulk
of the sample, which are much more numerous than surface nuclei.
However, nuclear spins on solid surfaces can be selectively polarized
by transferring spin polarization to them from hyperpolarized xenon
gas. This makes the surface signals strong enough to measure and
distinguish from bulk signals.
Other
=======
In nuclear energy studies, xenon is used in bubble chambers, probes,
and in other areas where a high molecular weight and inert chemistry
is desirable. A by-product of nuclear weapon testing is the release of
radioactive xenon-133 and xenon-135. These isotopes are monitored to
ensure compliance with nuclear test ban treaties, and to confirm
nuclear tests by states such as North Korea.
Liquid xenon is used in calorimeters to measure gamma rays, and as a
detector of hypothetical weakly interacting massive particles, or
WIMPs. When a WIMP collides with a xenon nucleus, theory predicts it
will impart enough energy to cause ionization and scintillation.
Liquid xenon is useful for these experiments because its density makes
dark matter interaction more likely and it permits a quiet detector
through self-shielding.
Xenon is the preferred propellant for ion propulsion of spacecraft
because it has low ionization potential per atomic weight and can be
stored as a liquid at near room temperature (under high pressure), yet
easily evaporated to feed the engine. Xenon is inert, 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 JPL's Deep
Space 1 probe, Europe's SMART-1 spacecraft and for the three ion
propulsion engines on NASA's Dawn Spacecraft.
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. 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 that can be used for solving the phase problem.
Precautions
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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.
The speed of sound in xenon gas (169 m/s) is less than that in air
because the average velocity of the heavy xenon atoms is less than
that of nitrogen and oxygen molecules in air. Hence, xenon vibrates
more slowly in the vocal cords when exhaled and produces lowered voice
tones (low-frequency-enhanced sounds, but the fundamental frequency or
pitch does not change), an effect opposite to the high-toned voice
produced in helium. Specifically, when the vocal tract is filled with
xenon gas, its natural resonant frequency becomes lower than when it
is filled with air. Thus, the low frequencies of the sound wave
produced by the same direct vibration of the vocal cords would be
enhanced, resulting in a change of the timbre of the sound amplified
by the vocal tract. Like helium, xenon does not satisfy the body's
need for oxygen, and it is both a simple asphyxiant and an anesthetic
more powerful than nitrous oxide; consequently, and because xenon is
expensive, many universities have prohibited the voice stunt as a
general chemistry demonstration. The gas sulfur hexafluoride is
similar to xenon in molecular weight (146 versus 131), less expensive,
and though an asphyxiant, not toxic or anesthetic; it is often
substituted in these demonstrations.
Dense gases such as xenon and sulfur hexafluoride can be breathed
safely when mixed with at least 20% oxygen. Xenon at 80% concentration
along with 20% oxygen rapidly produces the unconsciousness of general
anesthesia. 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 a person who
enters an area filled with an odorless, colorless gas may be
asphyxiated without warning. 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.
Water-soluble xenon compounds such as monosodium xenate are moderately
toxic, but have a very short half-life of the body - intravenously
injected xenate is reduced to elemental xenon in about a minute.
See also
======================================================================
* Buoyant levitation
* Noble gases
* Penning mixture
External links
======================================================================
* [
http://www.periodicvideos.com/videos/054.htm Xenon] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
http://wwwrcamnl.wr.usgs.gov/isoig/period/xe_iig.html USGS Periodic
Table - Xenon]
* [
http://environmentalchemistry.com/yogi/periodic/Xe.html
EnvironmentalChemistry.com - Xenon]
*
[
http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/ramsay-lecture.html
Sir William Ramsay's Nobel-Prize lecture (1904)]
License
=========
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License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Xenon
