Lg Xenon

[Cecelia Seiner]

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.[15] 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.[16][17][18]

Xenon is used in flash lamps[19] and arc lamps,[20] and as a general anesthetic.[21] The first excimer laser design used a xenon dimer molecule (Xe2) as the lasing medium,[22] and the earliest laser designs used xenon flash lamps as pumps.[23] Xenon is also used to search for hypothetical weakly interacting massive particles[24] and as a propellant for ion thrusters in spacecraft.[25]

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.[26] 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.[27]

Xenon was discovered in England by the Scottish chemist William Ramsay and English chemist Morris Travers on July 12, 1898,[28] shortly after their discovery of the elements krypton and neon. They found xenon in the residue left over from evaporating components of liquid air.[29][30] Ramsay suggested the name xenon for this gas from the Greek word ξένον xnon, neuter singular form of ξένος xnos, meaning 'foreign(er)', 'strange(r)', or 'guest'.[31][32] In 1902, Ramsay estimated the proportion of xenon in the Earth's atmosphere to be one part in 20 million.[33]

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.[19][34][35]

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.[36]

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.[49]

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.[50] As a liquid, xenon has a density of up to 3.100 g/mL, with the density maximum occurring at the triple point.[51] 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.[52] 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.[51] Under gigapascals of pressure, xenon forms a metallic phase.[53]

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.[54] It is completely metallic at 155 GPa.[55] 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.[54][better source needed]

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.[56]

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.[57]

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,[58] but the most intense lines occur in the region of blue light, producing the coloration.[59]

Xenon is a trace gas in Earth's atmosphere, occurring at a volume fraction of 871 nL/L (parts per billion), or approximately 1 part per 11.5 million.[60] It is also found as a component of gases emitted from some mineral springs. Given a total mass of the atmosphere of 5.151018 kilograms (1.1351019 lb), the atmosphere contains on the order of 2.03 gigatonnes (2.00109 long tons; 2.24109 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.

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.[69] Instead, xenon is formed during supernova explosions during the r-process,[70] by the slow neutron-capture process (s-process) in red giant stars that have exhausted their core hydrogen and entered the asymptotic giant branch,[71] and from radioactive decay, for example by beta decay of extinct iodine-129 and spontaneous fission of thorium, uranium, and plutonium.[72]

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.[73][74]

Stable or extremely long lived isotopes of xenon are also produced in appreciable quantities in nuclear fission. Xenon-136 is produced 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 and the absence of xenon-136 is a "fingerprint" for nuclear explosions, as xenon-135 is not produced directly but as a product of successive beta decays and thus it cannot absorb any neutrons in a nuclear explosion which occurs in fractions of a second.[75]

The stable isotope xenon-132 has a fission product yield of over 4% in the thermal neutron fission of 235
U 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.[76][77]

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.[81] 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).[82]

Some radioactive isotopes of xenon (for example, 133Xe and 135Xe) are produced by neutron irradiation of fissionable material within nuclear reactors.[16] 135Xe is of considerable significance in the operation of nuclear fission reactors. 135Xe has a huge cross section for thermal neutrons, 2.6106 barns,[27] 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).[87]

135Xe reactor poisoning was a major factor in the Chernobyl disaster.[88] 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,[89] or fissioning of uranium in cooling water.[90]

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