Editing Iron (section)

===Isotopes===
{{Main|Isotopes of iron}}
Iron has four stable [[isotope]]s: <sup>54</sup>Fe (5.845% of natural iron), [[iron-56|<sup>56</sup>Fe]] (91.754%), <sup>57</sup>Fe (2.119%) and <sup>58</sup>Fe (0.282%). Twenty-four artificial isotopes have also been created. Of these stable isotopes, only <sup>57</sup>Fe has a [[nuclear spin]] (−{{frac|1|2}}). The [[nuclide]] <sup>54</sup>Fe theoretically can undergo [[double beta decay|double electron capture]] to <sup>54</sup>Cr, but the process has never been observed and only a lower limit on the half-life of 4.4×10<sup>20</sup> years has been established.<ref>{{cite journal | last1=Bikit | first1=I. | last2=Krmar | first2=M. | last3=Slivka | first3=J. | last4=Vesković | first4=M. | last5=Čonkić | first5=Lj. | last6=Aničin | first6=I. | title=New results on the double β decay of iron | journal=Physical Review C | volume=58 | issue=4 | date=1998-10-01 | issn=0556-2813 | doi=10.1103/PhysRevC.58.2566 | pages=2566–2567| bibcode=1998PhRvC..58.2566B }}</ref>

<sup>60</sup>Fe is an [[extinct radionuclide]] of long [[half-life]] (2.6 million years).<ref name="RugelFaestermann2009">{{cite journal |last1=Rugel |first1=G. |last2=Faestermann |first2=T. |last3=Knie |first3=K. |last4=Korschinek |first4=G. |last5=Poutivtsev |first5=M. |last6=Schumann |first6=D. |last7=Kivel |first7=N. |last8=Günther-Leopold |first8=I. |last9=Weinreich |first9=R.|last10=Wohlmuther |first10=M. |title=New Measurement of the <sup>60</sup>Fe Half-Life |journal=Physical Review Letters |volume=103 |issue=7 |page=072502 |date=2009 |doi=10.1103/PhysRevLett.103.072502 |pmid=19792637 |bibcode=2009PhRvL.103g2502R |url=https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A17743/datastream/PDF/view}}</ref> It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide [[nickel-60|<sup>60</sup>Ni]].{{NUBASE2020|ref}} Much of the past work on isotopic composition of iron has focused on the [[nucleosynthesis]] of <sup>60</sup>Fe through studies of [[meteorite]]s and ore formation. In the last decade, advances in [[mass spectrometry]] have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the [[stable isotope]]s of iron. Much of this work is driven by the [[Earth science|Earth]] and [[planetary science]] communities, although applications to biological and industrial systems are emerging.<ref>{{Cite journal|last1=Dauphas|first1=N.|last2=Rouxel|first2=O.|date=2006|title=Mass spectrometry and natural variations of iron isotopes|journal=Mass Spectrometry Reviews |volume=25 |issue=4 |pages=515–50 |doi=10.1002/mas.20078 |url=https://geosci.uchicago.edu/~dauphas/OLwebsite/PDFfiles/Dauphas_Rouxel_MSR06.pdf |pmid=16463281 |bibcode=2006MSRv...25..515D |url-status=dead|archive-url=https://web.archive.org/web/20100610095913/https://geosci.uchicago.edu/~dauphas/OLwebsite/PDFfiles/Dauphas_Rouxel_MSR06.pdf |archive-date=10 June 2010}}</ref>

In phases of the meteorites ''Semarkona'' and ''Chervony Kut,'' a correlation between the concentration of <sup>60</sup>Ni, the [[daughter product|granddaughter]] of <sup>60</sup>Fe, and the abundance of the stable iron isotopes provided evidence for the existence of <sup>60</sup>Fe at the time of [[Formation and evolution of the Solar System|formation of the Solar System]]. Possibly the energy released by the decay of <sup>60</sup>Fe, along with that released by [[aluminium-26|<sup>26</sup>Al]], contributed to the remelting and [[planetary differentiation|differentiation]] of [[asteroid]]s after their formation 4.6 billion years ago. The abundance of <sup>60</sup>Ni present in [[wikt:extraterrestrial|extraterrestrial]] material may bring further insight into the origin and early history of the [[Solar System]].<ref>{{cite journal |title=Evidence for live 60Fe in meteorites |date=2004 |last1=Mostefaoui |first1=S. |last2=Lugmair |first2=G.W. |last3=Hoppe |first3=P. |last4=El Goresy |first4=A. |journal=New Astronomy Reviews |volume=48 |issue=1–4 |pages=155–59 |doi=10.1016/j.newar.2003.11.022 |bibcode=2004NewAR..48..155M}}</ref>

The most abundant iron isotope <sup>56</sup>Fe is of particular interest to nuclear scientists because it represents the most common endpoint of [[nucleosynthesis]].<ref>{{cite journal|last1=Fewell|first1=M. P.|title=The atomic nuclide with the highest mean binding energy |journal=American Journal of Physics|volume=63|issue=7 |page=653|date=1995|doi=10.1119/1.17828 |bibcode=1995AmJPh..63..653F}}</ref> Since <sup>56</sup>Ni (14 [[alpha particle]]s) is easily produced from lighter nuclei in the [[alpha process]] in [[nuclear reaction]]s in supernovae (see [[silicon burning process]]), it is the endpoint of fusion chains inside [[Population III stars|extremely massive stars]]. Although adding more alpha particles is possible, but nonetheless the sequence does effectively end at <sup>56</sup>Ni because conditions in stellar interiors cause the competition between [[photodisintegration]] and the alpha process to favor photodisintegration around <sup>56</sup>Ni.<ref>{{cite journal |last=Fewell |first=M.P. |date=1995-07-01 |title=The atomic nuclide with the highest mean binding energy |journal=American Journal of Physics |volume=63 |issue=7 |pages=653–658 |doi=10.1119/1.17828 |bibcode=1995AmJPh..63..653F |issn=0002-9505}}</ref><ref>{{cite journal |last1=Burbidge |first1=E. Margaret |author-link1=Margaret Burbidge |last2=Burbidge |first2=G.R. |author-link2=Geoffrey Burbidge |last3=Fowler |first3=William A. |author-link3=William Alfred Fowler |last4=Hoyle |first4=F. |author-link4=Fred Hoyle |date=1957-10-01 |title=Synthesis of the elements in stars |journal=Reviews of Modern Physics |volume=29 |issue=4 |pages=547–650 |bibcode=1957RvMP...29..547B |doi=10.1103/RevModPhys.29.547 |doi-access=free}}</ref> This <sup>56</sup>Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in the [[supernova remnant]] gas cloud, first to radioactive <sup>56</sup>Co, and then to stable <sup>56</sup>Fe. As such, iron is the most abundant element in the core of [[red giant]]s, and is the most abundant metal in [[iron meteorite]]s and in the dense metal [[Planetary core|cores of planets]] such as [[Earth]].{{sfn|Greenwood|Earnshaw|1997|p=12}} It is also very common in the universe, relative to other stable [[Metallicity|metals]] of approximately the same [[Atomic mass|atomic weight]].{{sfn|Greenwood|Earnshaw|1997|p=12}}<ref>{{cite journal |last1=Woosley |first1=S. |last2=Janka |first2=T. |title=The physics of core collapse supernovae |year=2006 |arxiv=astro-ph/0601261 |doi=10.1038/nphys172 |volume=1 |issue=3 |journal=Nature Physics |pages=147–54| bibcode=2005NatPh...1..147W |s2cid=118974639}}</ref> Iron is the sixth most [[Abundance of the chemical elements|abundant element]] in the [[universe]], and the most common [[refractory]] element.<ref name="apjl717_2_L92">{{cite journal
 | last1=McDonald | first1=I. | last2=Sloan | first2=G. C.
 | last3=Zijlstra | first3=A. A. | last4=Matsunaga | first4=N.
 | last5=Matsuura | first5=M. | last6=Kraemer | first6=K. E.
 | last7=Bernard-Salas | first7=J. | last8=Markwick | first8=A. J.
 | title=Rusty Old Stars: A Source of the Missing Interstellar Iron?
 | journal=The Astrophysical Journal Letters
 | volume=717 | issue=2 | pages=L92–L97 | date=2010
 | doi=10.1088/2041-8205/717/2/L92 | bibcode=2010ApJ...717L..92M |arxiv = 1005.3489 | s2cid=14437704 }}</ref>

[[File:Ironattenuation.PNG|thumb|upright=1.15|alt=A graph of attenuation coefficient vs. energy between 1 meV and 100 keV for several photon scattering mechanisms.|[[Photon]] [[mass attenuation coefficient]] for iron]]

Although a further tiny energy gain could be extracted by synthesizing [[nickel-62|<sup>62</sup>Ni]], which has a marginally higher binding energy than <sup>56</sup>Fe, conditions in stars are unsuitable for this process. Element production in supernovas greatly favor iron over nickel, and in any case, <sup>56</sup>Fe still has a lower mass per nucleon than <sup>62</sup>Ni due to its higher fraction of lighter protons.<ref>{{cite journal |title=Iron and Nickel Abundances in H~II Regions and Supernova Remnants |date=1995 |bibcode=1995AAS...186.3707B |last1=Bautista |first1= Manuel A. |last2=Pradhan |first2=Anil K. |journal=Bulletin of the American Astronomical Society |volume=27 |page=865}}</ref> Hence, elements heavier than iron require a [[supernova]] for their formation, involving [[r-process|rapid neutron capture]] by starting <sup>56</sup>Fe nuclei.{{sfn|Greenwood|Earnshaw|1997|p=12}}

In the [[timeline of the far future|far future]] of the universe, assuming that [[proton decay]] does not occur, cold [[nuclear fusion|fusion]] occurring via [[quantum tunnelling]] would cause the light nuclei in ordinary matter to fuse into <sup>56</sup>Fe nuclei. Fission and [[Alpha decay|alpha-particle emission]] would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron.<ref name="twoe">{{cite journal |title=Time without end: Physics and biology in an open universe |first=Freeman J. |last=Dyson |journal=[[Reviews of Modern Physics]] |volume=51 |issue=3 |year=1979 |pages=447–60 |doi=10.1103/RevModPhys.51.447 |bibcode = 1979RvMP...51..447D }}</ref>