Isotopes of iron

Main isotopes of Chemistry:iron (26Fe) | Iso­tope | Decay

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| abun­dance | half-life (t1/2) | mode | pro­duct
54Fe  | 5.85%  | stable
55Fe | syn | 2.73 y  | ε | 55Mn
56Fe | 91.75%  | stable
57Fe  | 2.12%  | stable
58Fe  | 0.28%  | stable
59Fe  | syn  | 44.6 d  | β− | 59Co
60Fe  | trace | 2.6×106 y  | β− | 60Co
Standard atomic weight Ar, standard(Fe)|

* 55.845(2)[1]

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Natural iron (26Fe) consists of four stable isotopes: 5.85% 54Fe, 91.75% 56Fe, 2.12% 57Fe and 0.28% 58Fe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are 60Fe (half-life 2.62 million years) and 55Fe (half-life 2.7562 years).

Much of the past work on measuring the isotopic composition of iron has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (e.g., 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, though applications to biological and industrial systems are beginning to emerge.[2]

## Contents

* 1 List of isotopes
* 2 Iron-56
* 3 Iron-57
* 4 Iron-60
* 5 See also
* 6 References
* 7 Further reading

## List of isotopes

Nuclide
[n 1] | Z | N | Isotopic mass (u)
[n 2][n 3] | Half-life
[n 4] | Decay
mode
[n 5] | Daughter
isotope
[n 6] | Spin and
parity
[n 7][n 4] | Physics:Natural abundance (mole fraction)

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Excitation energy  | Normal proportion  | 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+  |  |

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. ↑ 4.0 4.1 # - 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

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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[3]
9. ↑ Lowest mass per nucleon of all nuclides; End product of stellar nucleosynthesis

## Iron-56

Main article: Physics: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.[4] However, because of the details of how nucleosynthesis works, 56Fe is a more common endpoint of fusion inside supernovae, where it is mostly produced as 56Ni, which subsequently decays to 56Co and then iron. Thus, 56Fe is more common in the universe, relative to other heavy elements, including 62Ni, 58Fe, and 60Ni, all of which have a comparably high binding energy.

## Iron-57

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.[5] The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound–Rebka experiment.[6]

## Iron-60

Iron-60 has a half-life of 2.62 million years,[7] but was thought until 2009 to have a half-life of 1.5 million years. It undergoes beta decay to 60Co, which then decays with the much shorter half-life of about 5 years to stable 60Ni.

In phases of the meteorites Semarkona and Chervony Kut, a correlation between the excess 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.[8] Depending on its original abundance, the energy from the decay of 60Fe may have been significant, along with that of 26Al, to the remelting and differentiation of asteroids and planetesimals after their formation. These nickel abundances in extraterrestrial materials may also provide further insight into the origin of the Solar System and its early history.

Live (interstellar) iron-60 was first identified in deep sea sediments in 1999.[9] These are deep sea ferromanganese crusts, which are constantly growing, aggregating iron, manganese, and other elements.[10] Iron-60 has been found in fossilized bacteria in sea floor sediments.[11][12] In 2019, researchers found 60Fe in Antarctica.[13] Iron-60 shows two peaks in deep sea sediments, the first 1.7–3.2 million years ago and the second 6.5–8.7 million years ago. The peaks are relate to the passage of the Solar System through the Local Bubble and likely the Orion–Eridanus Superbubble. These superbubbles were created by multiple supernovae.[14] Traces of iron-60 have also been found in lunar samples.

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 surface area 4πr2. The fraction of the material intercepted by the Earth is dependent on its cross-sectional area (Template:Subsup) as it passes through the expanding debris:

MFraction intercepted =πREarth 24πr2Mej

where Mej is the mass of ejected material. Assuming the intercepted material is distributed uniformly across the surface of the Earth (Template:Subsup), the mass surface density (Σej) of the supernova ejecta on Earth is:

Σej=MFraction intercepted Asurface,Earth =Mej16πr2

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.

N60=(Mej,60/m6016πr2)

The equation for N60 can be rearranged to find the distance to the supernova.

r=Mej,6016πm60N60

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 atoms/m2) and a rough estimate of the mass of 60Fe ejected by a supernova (10×10−5 M☉).

r=10−5M⊙16π(60mp)N60r=3×1018m=100pc

More sophisticated analyses have been reported that take into consideration the flux and deposition of 60Fe as well as possible interfering background sources.[15]

Cobalt-60, the decay product of iron-60, emits 1.173 MeV and 1.332 MeV gamma rays as it decays. These 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.[16][17]

## See also

Daughter products other than iron

* Isotopes of cobalt
* Isotopes of manganese
* Isotopes of chromium
* Isotopes of vanadium

## References

1. ↑ Meija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; De Bièvre, Paul; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. ↑ N. Dauphas; O. Rouxel (2006). "Mass spectrometry and natural variations of iron isotopes". Mass Spectrometry Reviews 25 (4): 515–550. doi:10.1002/mas.20078. PMID 16463281. Bibcode: 2006MSRv...25..515D.
3. ↑ 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. doi:10.1103/PhysRevC.58.2566. Bibcode: 1998PhRvC..58.2566B.
4. ↑ Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics 63 (7): 653. doi:10.1119/1.17828. Bibcode: 1995AmJPh..63..653F. https://ui.adsabs.harvard.edu/abs/1995AmJPh..63..653F/abstract.
5. ↑ R. Nave. "Mossbauer Effect in Iron-57". HyperPhysics. Georgia State University. http://hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear/mossfe.html.
6. ↑ Pound, R. V.; Rebka Jr. G. A. (April 1, 1960). "Apparent weight of photons". Physical Review Letters 4 (7): 337–341. doi:10.1103/PhysRevLett.4.337. Bibcode: 1960PhRvL...4..337P.
7. ↑ Rugel, G.; Faestermann, T.; Knie, K.; Korschinek, G.; Poutivtsev, M.; Schumann, D.; Kivel, N.; Günther-Leopold, I. et al. (2009). "New Measurement of the 60Fe Half-Life". Physical Review Letters 103 (7). doi:10.1103/PhysRevLett.103.072502. PMID 19792637. Bibcode: 2009PhRvL.103g2502R. https://www.dora.lib4ri.ch/psi/islandora/object/psi:17743.
8. ↑ Mostefaoui, S.; Lugmair, G.W.; Hoppe, P.; El Goresy, A. (2004). "Evidence for live 60Fe in meteorites". New Astronomy Reviews 48 (1–4): 155–59. doi:10.1016/j.newar.2003.11.022. Bibcode: 2004NewAR..48..155M.
9. ↑ Knie, K.; Korschinek, G.; Faestermann, T.; Wallner, C.; Scholten, J.; Hillebrandt, W. (1999-07-01). "Indication for Supernova Produced 60Fe Activity on Earth". Physical Review Letters 83 (1): 18–21. doi:10.1103/PhysRevLett.83.18. ISSN 0031-9007. Bibcode: 1999PhRvL..83...18K. https://ui.adsabs.harvard.edu/abs/1999PhRvL..83...18K.
10. ↑ Wallner, A.; Froehlich, M. B.; Hotchkis, M. A. C.; Kinoshita, N.; Paul, M.; Martschini, M.; Pavetich, S.; Tims, S. G. et al. (2021-05-01). "60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae". Science 372 (6543): 742–745. doi:10.1126/science.aax3972. ISSN 0036-8075. PMID 33986180. Bibcode: 2021Sci...372..742W. https://ui.adsabs.harvard.edu/abs/2021Sci...372..742W.
11. ↑ Smith, Belinda (August 9, 2016). "Ancient bacteria store signs of supernova smattering". Cosmos. https://cosmosmagazine.com/space/ancient-bacteria-store-signs-of-supernova-smattering.
12. ↑ Ludwig, Peter (August 16, 2016). "Time-resolved 2-million-year-old supernova activity discovered in Earth's microfossil record". PNAS 113 (33): 9232–9237. doi:10.1073/pnas.1601040113. PMID 27503888. Bibcode: 2016PNAS..113.9232L.
13. ↑ Koll, Dominik (2019). "Interstellar 60Fe in Antarctica". Physical Review Letters 123 (7). doi:10.1103/PhysRevLett.123.072701. PMID 31491090. Bibcode: 2019PhRvL.123g2701K.
14. ↑ Schulreich, M. M.; Feige, J.; Breitschwerdt, D. (2023-12-01). "Numerical studies on the link between radioisotopic signatures on Earth and the formation of the Local Bubble. II. Advanced modelling of interstellar 26Al, 53Mn, 60Fe, and 244Pu influxes as traces of past supernova activity in the solar neighbourhood". Astronomy and Astrophysics 680: A39. doi:10.1051/0004-6361/202347532. ISSN 0004-6361. Bibcode: 2023A&A...680A..39S. https://ui.adsabs.harvard.edu/abs/2023A&A...680A..39S.
15. ↑ 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. doi:10.3847/1538-4357/acb699.
16. ↑ Harris, M. J.; Knödlseder, J.; Jean, P.; Cisana, E.; Diehl, R.; Lichti, G. G.; Roques, J.-P.; Schanne, S. et al. (2005-04-01). "Detection of γ-ray lines from interstellar 60Fe by the high resolution spectrometer SPI". Astronomy and Astrophysics 433 (3): L49–L52. doi:10.1051/0004-6361:200500093. ISSN 0004-6361. Bibcode: 2005A&A...433L..49H. https://ui.adsabs.harvard.edu/abs/2005A&A...433L..49H.
17. ↑ Wang, W.; Siegert, T.; Dai, Z. G.; Diehl, R.; Greiner, J.; Heger, A.; Krause, M.; Lang, M. et al. (2020-02-01). "Gamma-Ray Emission of 60Fe and 26Al Radioactivity in Our Galaxy". The Astrophysical Journal 889 (2): 169. doi:10.3847/1538-4357/ab6336. ISSN 0004-637X. Bibcode: 2020ApJ...889..169W.

## Further reading

* J. M. Nielsen (1960). The Radiochemistry of Iron. National Academy of Sciences/National Research Council. http://library.lanl.gov/cgi-bin/getfile?rc000015.pdf.

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