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Isotopes of iron

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Naturally occurring iron (26Fe) consists of four stable isotopes: 5.845% of 54Fe (possibly radioactive with a half-life over 4.4×1020 years),[4] 91.754% of 56Fe, 2.119% of 57Fe and 0.286% of 58Fe. There are 28 known radioactive isotopes and 8 nuclear isomers, the most stable of which are 60Fe (half-life 2.6 million years) and 55Fe (half-life 2.7 years).

Isotopes of iron (26Fe)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
54Fe 5.85% stable
55Fe synth 2.73 y ε 55Mn
56Fe 91.8% stable
57Fe 2.12% stable
58Fe 0.28% stable
59Fe synth 44.6 d β− 59Co
60Fe trace 2.6×106 y β− 60Co
Standard atomic weight Ar°(Fe)

Much of the past work on measuring the isotopic composition of iron has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge.[5]

List of isotopes

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Nuclide
[n 1] 		Z N Isotopic mass (Da)[6]
[n 2][n 3] 		Half-life[1]
[n 4] 		Decay
mode[1]
[n 5] 		Daughter
isotope
[n 6] 		Spin and
parity[1]
[n 7][n 4] 		Natural abundance (mole fraction)
Excitation energy Normal proportion[1] Range of variation
45Fe 26 19 45.01547(30)# 2.5(2) ms 2p (70%) 43Cr 3/2 #
β , p (18.9%) 44Cr
β , 2p (7.8%) 43V
β (3.3%) 45Mn
46Fe 26 20 46.00130(32)# 13.0(20) ms β , p (78.7%) 45Cr 0
β (21.3%) 46Mn
β , 2p? 44V
47Fe 26 21 46.99235(54)# 21.9(2) ms β , p (88.4%) 46Cr 7/2−#
β (11.6%) 47Mn
48Fe 26 22 47.980667(99) 45.3(6) ms β (84.7%) 48Mn 0
β , p (15.3%) 47Cr
49Fe 26 23 48.973429(26) 64.7(3) ms β , p (56.7%) 48Cr (7/2−)
β (43.3%) 49Mn
50Fe 26 24 49.9629880(90) 152.0(6) ms β 50Mn 0
β , p? 49Cr
51Fe 26 25 50.9568551(15) 305.4(23) ms β 51Mn 5/2−
52Fe 26 26 51.94811336(19) 8.275(8) h β 52Mn 0
52mFe 6960.7(3) keV 45.9(6) s β (99.98%) 52Mn 12
IT (0.021%) 52Fe
53Fe 26 27 52.9453056(18) 8.51(2) min β 53Mn 7/2−
53mFe 3040.4(3) keV 2.54(2) min IT 53Fe 19/2−
54Fe 26 28 53.93960819(37) Observationally Stable[n 8] 0 0.05845(105)
54mFe 6527.1(11) keV 364(7) ns IT 54Fe 10
55Fe 26 29 54.93829116(33) 2.7562(4) y EC 55Mn 3/2−
56Fe[n 9] 26 30 55.93493554(29) Stable 0 0.91754(106)
57Fe 26 31 56.93539195(29) Stable 1/2− 0.02119(29)
58Fe 26 32 57.93327358(34) Stable 0 0.00282(12)
59Fe 26 33 58.93487349(35) 44.500(12) d β− 59Co 3/2−
60Fe 26 34 59.9340702(37) 2.62(4)×106 y β− 60Co 0 trace
61Fe 26 35 60.9367462(28) 5.98(6) min β− 61Co (3/2−)
61mFe 861.67(11) keV 238(5) ns IT 61Fe 9/2
62Fe 26 36 61.9367918(30) 68(2) s β− 62Co 0
63Fe 26 37 62.9402727(46) 6.1(6) s β− 63Co (5/2−)
64Fe 26 38 63.9409878(54) 2.0(2) s β− 64Co 0
65Fe 26 39 64.9450153(55) 805(10) ms β− 65Co (1/2−)
β−, n? 64Co
65m1Fe 393.7(2) keV 1.12(15) s β−? 65Co (9/2 )
65m2Fe 397.6(2) keV 418(12) ns IT 65Fe (5/2 )
66Fe 26 40 65.9462500(44) 467(29) ms β− 66Co 0
β−, n? 65Co
67Fe 26 41 66.9509300(41) 394(9) ms β− 67Co (1/2-)
β−, n? 66Co
67m1Fe 403(9) keV 64(17) μs IT 67Fe (5/2 ,7/2 )
67m2Fe 450(100)# keV 75(21) μs IT 67Fe (9/2 )
68Fe 26 42 67.95288(21)# 188(4) ms β− 68Co 0
β−, n? 67Co
69Fe 26 43 68.95792(22)# 162(7) ms β− 69Co 1/2−#
β−, n? 68Co
β−, 2n? 67Co
70Fe 26 44 69.96040(32)# 61.4(7) ms β− 70Co 0
β−, n? 69Co
71Fe 26 45 70.96572(43)# 34.3(26) ms β− 71Co 7/2 #
β−, n? 70Co
β−, 2n? 69Co
72Fe 26 46 71.96860(54)# 17.0(10) ms β− 72Co 0
β−, n? 71Co
β−, 2n? 70Co
73Fe 26 47 72.97425(54)# 12.9(16) ms β− 73Co 7/2 #
β−, n? 72Co
β−, 2n? 71Co
74Fe 26 48 73.97782(54)# 5(5) ms β− 74Co 0
β−, n? 73Co
β−, 2n? 72Co
75Fe 26 49 74.98422(64)# 9# ms
[>620 ns] 		β−? 75Co 9/2 #
β−, n? 74Co
β−, 2n? 73Co
76Fe 26 50 75.98863(64)# 3# ms
[>410 ns] 		β−? 76Co 0
This table header & footer:
  1. ^ mFe – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ a b # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. ^ Modes of decay:
    EC: Electron capture
    IT: Isomeric transition
    n: Neutron emission
    p: Proton emission
  6. ^ Bold symbol as daughter – Daughter product is stable.
  7. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  8. ^ Believed to decay by β β to 54Cr with a half-life of over 4.4×1020 a[4]
  9. ^ Lowest mass per nucleon of all nuclides; End product of stellar nucleosynthesis

Iron-54

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54Fe is observationally stable, but theoretically can decay to 54Cr, with a half-life of more than 4.4×1020 years via double electron capture (εε).[4]

Iron-56

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Main article: Iron-56

56Fe is the most abundant isotope of iron. It is also the isotope with the lowest mass per nucleon, 930.412 MeV/c2, though not the isotope with the highest nuclear binding energy per nucleon, which is nickel-62.[7] However, because of the details of how nucleosynthesis works, 56Fe is a more common endpoint of fusion chains inside supernovae, where it is mostly produced as 56Ni. Thus, 56Ni is more common in the universe, relative to other metals, including 62Ni, 58Fe and 60Ni, all of which have a very high binding energy.

The high nuclear binding energy for 56Fe represents the point where further nuclear reactions become energetically unfavorable. Because of this, it is among the heaviest elements formed in stellar nucleosynthesis reactions in massive stars. These reactions fuse lighter elements like magnesium, silicon, and sulfur to form heavier elements. Among the heavier elements formed is 56Ni, which subsequently decays to 56Co and then 56Fe.

Iron-57

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57Fe is widely used in Mössbauer spectroscopy and the related nuclear resonance vibrational spectroscopy due to the low natural variation in energy of the 14.4 keV nuclear transition.[8] The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound–Rebka experiment.[9]

Iron-58

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Iron-58 can be used to combat anemia and low iron absorption, to metabolically track iron-controlling human genes, and for tracing elements in nature.[10][11] Iron-58 is also an assisting reagent in the synthesis of superheavy elements.[11]

Iron-60

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Iron-60 is an iron isotope with a half-life of 2.6 million years,[12][13] but was thought until 2009 to have a half-life of 1.5 million years. It undergoes beta decay to cobalt-60, which then decays with a half-life of about 5 years to stable nickel-60. Traces of iron-60 have been found in lunar samples.

In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni, the granddaughter isotope of 60Fe, and the abundance of the stable iron isotopes could be found, which is evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26Al, to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the Solar System and its early history.

Iron-60 found in fossilised bacteria in sea floor sediments suggest there was a supernova in the vicinity of the Solar System approximately 2 million years ago.[14][15] Iron-60 is also found in sediments from 8 million years ago.[16] In 2019, researchers found interstellar 60Fe in Antarctica, which they relate to the Local Interstellar Cloud.[17]

The distance to the supernova of origin can be estimated by relating the amount of iron-60 intercepted as Earth passes through the expanding supernova ejecta. Assuming that the material ejected in a supernova expands uniformly out from its origin as a sphere with a surface area of 4πr2. The fraction of the material intercepted by the Earth is dependent on its cross-sectional area (πR2earth) as it passes through the expanding debris. Where Mej is the mass of ejected material. Assuming the intercepted material is distributed uniformly across the surface of the Earth (4πR2earth), the mass surface density (Σej) of the supernova ejecta on Earth is:  The number of 60Fe atoms per unit area found on Earth can be estimated if the typical amount of 60Fe ejected from a supernova is known. This can be done by dividing the surface mass density (Σej) by the atomic mass of 60Fe.  The equation for N60 can be rearranged to find the distance to the supernova. An example calculation for the distance to the supernova point of origin is given below. This calculation uses speculative values for terrestrial 60Fe atom surface density (N60 ≈ 4 × 1011 atoms2/m) and a rough estimate of the mass of 60Fe ejected in a supernova explosion (10-5 M☉).   More sophisticated analyses have been reported that take into consideration the flux and deposition of 60Fe as well as possible interfering background sources.[18]

Cobalt-60, the decay product of iron-60, emits 1.173 MeV and 1.333 MeV as it decays. These gamma-ray lines have long been important targets for gamma-ray astronomy, and have been detected by the gamma-ray observatory INTEGRAL. The signal traces the Galactic plane, showing that 60Fe synthesis is ongoing in our Galaxy, and probing element production in massive stars.[19][20]

References

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  1. ^ a b c d e Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. ^ "Standard Atomic Weights: Iron". CIAAW. 1993.
  3. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. ^ a b c Bikit, I.; Krmar, M.; Slivka, J.; Vesković, M.; Čonkić, Lj.; Aničin, I. (1998). "New results on the double β decay of iron". Physical Review C. 58 (4): 2566–2567. Bibcode:1998PhRvC..58.2566B. doi:10.1103/PhysRevC.58.2566.
  5. ^ N. Dauphas; O. Rouxel (2006). "Mass spectrometry and natural variations of iron isotopes". Mass Spectrometry Reviews. 25 (4): 515–550. Bibcode:2006MSRv...25..515D. doi:10.1002/mas.20078. PMID 16463281.
  6. ^ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
  7. ^ Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics. 63 (7): 653. Bibcode:1995AmJPh..63..653F. doi:10.1119/1.17828.
  8. ^ R. Nave. "Mossbauer Effect in Iron-57". HyperPhysics. Georgia State University. Retrieved 2009-10-13.
  9. ^ Pound, R. V.; Rebka Jr. G. A. (April 1, 1960). "Apparent weight of photons". Physical Review Letters. 4 (7): 337–341. Bibcode:1960PhRvL...4..337P. doi:10.1103/PhysRevLett.4.337.
  10. ^ "Iron-58 Metal Isotope". American Elements. Retrieved 2023-06-28.
  11. ^ a b Vasiliev, Petr. "Iron-58, Iron-58 Isotope, Enriched Iron-58, Iron-58 Metal". www.buyisotope.com. Retrieved 2023-06-28.
  12. ^ Rugel, G.; Faestermann, T.; Knie, K.; Korschinek, G.; Poutivtsev, M.; Schumann, D.; Kivel, N.; Günther-Leopold, I.; Weinreich, R.; Wohlmuther, M. (2009). "New Measurement of the 60Fe Half-Life". Physical Review Letters. 103 (7): 72502. Bibcode:2009PhRvL.103g2502R. doi:10.1103/PhysRevLett.103.072502. PMID 19792637.
  13. ^ "Eisen mit langem Atem". scienceticker. 27 August 2009. Archived from the original on 3 February 2018. Retrieved 22 May 2010.
  14. ^ Belinda Smith (Aug 9, 2016). "Ancient bacteria store signs of supernova smattering". Cosmos.
  15. ^ Peter Ludwig; et al. (Aug 16, 2016). "Time-resolved 2-million-year-old supernova activity discovered in Earth's microfossil record". PNAS. 113 (33): 9232–9237. arXiv:1710.09573. Bibcode:2016PNAS..113.9232L. doi:10.1073/pnas.1601040113. PMC 4995991. PMID 27503888.
  16. ^ Colin Barras (Oct 14, 2017). "Fires may have given our evolution a kick-start". New Scientist. 236 (3147): 7. Bibcode:2017NewSc.236....7B. doi:10.1016/S0262-4079(17)31997-8.
  17. ^ Koll, Dominik; et., al. (2019). "Interstellar 60Fe in Antarctica". Physical Review Letters. 123 (7): 072701. Bibcode:2019PhRvL.123g2701K. doi:10.1103/PhysRevLett.123.072701. hdl:1885/298253. PMID 31491090. S2CID 201868513.
  18. ^ Ertel, Adrienne F.; Fry, Brian J.; Fields, Brian D.; Ellis, John (20 April 2023). "Supernova Dust Evolution Probed by Deep-sea 60Fe Time History". The Astrophysical Journal. 947 (2): 58–83 – via The Institute of Physics (IOP).
  19. ^ Harris, M. J.; Knödlseder, J.; Jean, P.; Cisana, E.; Diehl, R.; Lichti, G. G.; Roques, J. -P.; Schanne, S.; Weidenspointner, G. (2005-04-01). "Detection of γ-ray lines from interstellar 60Fe by the high resolution spectrometer SPI". Astronomy and Astrophysics. 433 (3): L49–L52. arXiv:astro-ph/0502219. Bibcode:2005A&A...433L..49H. doi:10.1051/0004-6361:200500093. ISSN 0004-6361.
  20. ^ Wang, W.; Siegert, T.; Dai, Z. G.; Diehl, R.; Greiner, J.; Heger, A.; Krause, M.; Lang, M.; Pleintinger, M. M. M.; Zhang, X. L. (2020-02-01). "Gamma-Ray Emission of 60Fe and 26Al Radioactivity in Our Galaxy". The Astrophysical Journal. 889 (2): 169. arXiv:1912.07874. Bibcode:2020ApJ...889..169W. doi:10.3847/1538-4357/ab6336. ISSN 0004-637X.

Isotope masses from:

Isotopic compositions and standard atomic masses from:

Half-life, spin, and isomer data selected from:

Further reading

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