Noble gas
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.
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 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 trace gas in Earth's atmosphere, occurring at a volume fraction of 87±1 nL/L (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 5.15×1018 kilograms (1.135×1019 lb), the atmosphere contains on the order of 2.03 gigatonnes (2.00×109 long tons; 2.24×109 short tons) 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 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 of xenon dioxide in silica, and reactions between Xe and Fe/Ni in the Earth's core.
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. …
Although xenon is rare and relatively expensive to extract from the Earth's atmosphere, it has a number of applications.
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. …
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 also 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 1.1×1022 yr, and 136Xe, which undergoes double beta decay with a half-life of 2.18×1021 yr.
129Xe is produced by beta decay of 129I, which has a half-life of 16.1 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.
Nuclei of the stable isotopes with odd mass number, 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). …
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. …