Isotopes of iron

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 24 known radioactive isotopes, 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 2.6×10^6 y β^− ^60Co
Standard atomic weight Ar°(Fe)
	55.845±0.002^[2] 55.845±0.002 (abridged)^[3]
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Much of the past work on measuring the isotopic composition of Fe 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

Nuclide ^[n 1]	Z	N	Isotopic mass (Da) ^[n 2]^[n 3]	Half-life ^[n 4]	Decay mode ^[n 5]	Daughter isotope ^[n 6]	Spin and parity ^[n 7]^[n 4]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion	Range of variation
^45Fe	26	19	45.01458(24)#	1.89(49) ms	β^+ (30%)	^45Mn	3/2+#
					2p (70%)	^43Cr
^46Fe	26	20	46.00081(38)#	9(4) ms [12(+4-3) ms]	β^+ (>99.9%)	^46Mn	0+
					β^+, p (<.1%)	^45Cr
^47Fe	26	21	46.99289(28)#	21.8(7) ms	β^+ (>99.9%)	^47Mn	7/2−#
					β^+, p (<.1%)	^46Cr
^48Fe	26	22	47.98050(8)#	44(7) ms	β^+ (96.41%)	^48Mn	0+
					β^+, p (3.59%)	^47Cr
^49Fe	26	23	48.97361(16)#	70(3) ms	β^+, p (52%)	^48Cr	(7/2−)
					β^+ (48%)	^49Mn
^50Fe	26	24	49.96299(6)	155(11) ms	β^+ (>99.9%)	^50Mn	0+
					β^+, p (<.1%)	^49Cr
^51Fe	26	25	50.956820(16)	305(5) ms	β^+	^51Mn	5/2−
^52Fe	26	26	51.948114(7)	8.275(8) h	β^+	^52mMn	0+
^52mFe	6.81(13) MeV			45.9(6) s	β^+	^52Mn	(12+)#
^53Fe	26	27	52.9453079(19)	8.51(2) min	β^+	^53Mn	7/2−
^53mFe	3040.4(3) keV			2.526(24) min	IT	^53Fe	19/2−
^54Fe	26	28	53.9396090(5)	Observationally Stable^[n 8]			0+	0.05845(35)	0.05837–0.05861
^54mFe	6526.9(6) keV			364(7) ns			10+
^55Fe	26	29	54.9382934(7)	2.737(11) y	EC	^55Mn	3/2−
^56Fe^[n 9]	26	30	55.9349363(5)	Stable			0+	0.91754(36)	0.91742–0.91760
^57Fe	26	31	56.9353928(5)	Stable			1/2−	0.02119(10)	0.02116–0.02121
^58Fe	26	32	57.9332744(5)	Stable			0+	0.00282(4)	0.00281–0.00282
^59Fe	26	33	58.9348755(8)	44.495(9) d	β^−	^59Co	3/2−
^60Fe	26	34	59.934072(4)	2.6×10^6 y	β^−	^60Co	0+	trace
^61Fe	26	35	60.936745(21)	5.98(6) min	β^−	^61Co	3/2−,5/2−
^61mFe	861(3) keV			250(10) ns			9/2+#
^62Fe	26	36	61.936767(16)	68(2) s	β^−	^62Co	0+
^63Fe	26	37	62.94037(18)	6.1(6) s	β^−	^63Co	(5/2)−
^64Fe	26	38	63.9412(3)	2.0(2) s	β^−	^64Co	0+
^65Fe	26	39	64.94538(26)	1.3(3) s	β^−	^65Co	1/2−#
^65mFe	364(3) keV			430(130) ns			(5/2−)
^66Fe	26	40	65.94678(32)	440(40) ms	β^− (>99.9%)	^66Co	0+
					β^−, n (<.1%)	^65Co
^67Fe	26	41	66.95095(45)	394(9) ms	β^− (>99.9%)	^67Co	1/2−#
					β^−, n (<.1%)	^66Co
^67mFe	367(3) keV			64(17) µs			(5/2−)
^68Fe	26	42	67.95370(75)	187(6) ms	β^− (>99.9%)	^68Co	0+
					β^−, n	^67Co
^69Fe	26	43	68.95878(54)#	109(9) ms	β^− (>99.9%)	^69Co	1/2−#
					β^−, n (<.1%)	^68Co
^70Fe	26	44	69.96146(64)#	94(17) ms			0+
^71Fe	26	45	70.96672(86)#	30# ms [>300 ns]			7/2+#
^72Fe	26	46	71.96962(86)#	10# ms [>300 ns]			0+
This table header & footer: view

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. # – 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

• Atomic masses of the stable nuclides (⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe, and ⁵⁸Fe) are given by the AME2012 atomic mass evaluation. The one standard deviation errors are given in parentheses after the corresponding last digits.^[6]

Iron-54

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

Main article: Iron-56

⁵⁶Fe is 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 extremely massive stars and is therefore more common in the universe, relative to other metals, including ⁶²Ni, ⁵⁸Fe and ⁶⁰Ni, all of which have a very 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.^[8] The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound–Rebka experiment.^[9]

Iron-58

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

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]

References

1. 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. 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, M.; Audi, G.; Wapstra, A.H.; Kondev, F.G.; MacCormick, M.; Xu, X.; Pfeiffer, B. (2012). "The Ame2012 atomic mass evaluation". Chinese Physics C. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003. hdl:11858/00-001M-0000-0010-23E8-5. S2CID 250839471.
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. 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. . 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.

Isotope masses from:

• 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

Isotopic compositions and standard atomic masses from:

• de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
• Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.
• "News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.

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

• 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, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.

Further reading

• J. M. Nielsen (1960). The Radiochemistry of Iron (PDF). National Academy of Sciences/National Research Council.