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Naturally occurring xenon (₅₄Xe) is made of eight stable isotopes and one very long-lived isotope. (¹²⁴Xe, ¹²⁶Xe, and ¹³⁴Xe are predicted to undergo double beta decay,^[3] but this has never been observed in these isotopes, so they are considered to be stable.)^[4][5]
Xenon has the second-highest number of stable isotopes. Only tin, with 10 stable isotopes, has more.^[6] Beyond these stable forms, 32 unstable isotopes and various isomers have been studied, the longest-lived of which is ¹³⁶Xe, which undergoes double beta decay with a half-life of 2.165 ± 0.016(stat) ± 0.059(sys) ×10²¹ years^[1] with the next longest lived being ¹²⁷Xe with a half-life of 36.345 days. All other isotopes have half-lives less than 12 days, most less than 20 hours. The shortest-lived isotope, ¹⁰⁸Xe,^[7] has a half-life of 58 µs, and is the heaviest known nuclide with equal numbers of protons and neutrons. Of known isomers, the longest-lived is ^131mXe with a half-life of 11.934 days. ¹²⁹Xe is produced by beta decay of ¹²⁹I (half-life: 16 million years); ^131mXe, ¹³³Xe, ^133mXe, and ¹³⁵Xe are some of the fission products of both ²³⁵U and ²³⁹Pu, so are used as indicators of nuclear explosions.

The artificial isotope ¹³⁵Xe is of considerable significance in the operation of nuclear fission reactors. ¹³⁵Xe has a huge cross section for thermal neutrons, 2.65×10⁶barns, so it acts as a neutron absorber or "poison" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production. 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).

Relatively high concentrations of radioactive xenon isotopes are also found emanating from nuclear reactors due to the release of this fission gas from cracked fuel rods or fissioning of uranium in cooling water.^{[citation needed]} The concentrations of these isotopes are still usually low compared to the naturally occurring radioactive noble gas ²²²Rn.

Because xenon is a tracer for two parent isotopes, Xe isotope ratios in meteorites are a powerful tool for studying the formation of the solar system. The I-Xe method of dating gives the time elapsed between nucleosynthesis and the condensation of a solid object from the solar nebula (xenon being a gas, only that part of it that formed after condensation will be present inside the object). Xenon isotopes are also a powerful tool for understanding terrestrial differentiation. Excess ¹²⁹Xe found in carbon dioxide well gases from New Mexico was believed to be from the decay of mantle-derived gases soon after Earth's formation.^[8]

Xenon-133

Xenon-133 (sold as a drug under the brand name Xeneisol, ATC code V09EX03 (WHO)) is an isotope of xenon. It is a radionuclide that is inhaled to assess pulmonary function, and to image the lungs.^[9] It is also used to image blood flow, particularly in the brain.^[10]133Xe is also an important fission product.^{[citation needed]} It is discharged to the atmosphere in small quantities by some nuclear power plants.^[11]

Xenon-135

Xenon-135 is a radioactive isotope of xenon, produced as a fission product of uranium. It has a half-life of about 9.2 hours and is the most powerful known neutron-absorbing nuclear poison (having a neutron absorption cross-section of 2 million barns^[12]). The overall yield of xenon-135 from fission is 6.3%, though most of this results from the radioactive decay of fission-produced tellurium-135 and iodine-135. Xe-135 exerts a significant effect on nuclear reactor operation (xenon pit). It is discharged to the atmosphere in small quantities by some nuclear power plants.^[11]

Xenon-136

Xenon-136 is an isotope of xenon that undergoes double beta decay to barium-136 with a very long half life of 2.11×10²¹ years, more than 10 orders of magnitude longer than the age of the universe ((13.799±0.021)×10⁹ years).

List of isotopes

Notes

• The isotopic composition refers to that in air.


• Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.


• Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.


• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.


• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

• Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).


• Isotopic compositions and standard atomic masses from:
  
  • 
    J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
    
  
  
  • 
    M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
    
  
  


• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  
  • 
    Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
    
  
  
  • 
    National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
    
  
  
  • 
    Holden, N. E. (2004). "11. Table of the Isotopes". In Lide, David R. CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.