Isotopes of iron - Reference.org

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Isotopes of iron

Nuclides with atomic number of 26, but with differing mass numbers

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

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, though applications to biological and industrial systems are beginning to emerge.

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List of isotopes

Nuclide³	Z	N	Isotopic mass (Da)⁴ ⁵ ⁶	Half-life ⁷ ⁸	Decaymode ⁹ ¹⁰	Daughterisotope ¹¹	Spin andparity ¹² ¹³ ¹⁴	Natural abundance (mole fraction)
Nuclide³	Excitation energy			Half-life ⁷ ⁸	Decaymode ⁹ ¹⁰	Daughterisotope ¹¹	Spin andparity ¹² ¹³ ¹⁴	Normal proportion¹⁵	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−#
47Fe	26	21	46.99235(54)#	21.9(2) ms	β+ (11.6%)	47Mn	7/2−#
48Fe	26	22	47.980667(99)	45.3(6) ms	β+ (84.7%)	48Mn	0+
48Fe	26	22	47.980667(99)	45.3(6) ms	β+, p (15.3%)	47Cr	0+
49Fe	26	23	48.973429(26)	64.7(3) ms	β+, p (56.7%)	48Cr	(7/2−)
49Fe	26	23	48.973429(26)	64.7(3) ms	β+ (43.3%)	49Mn	(7/2−)
50Fe	26	24	49.9629880(90)	152.0(6) ms	β+	50Mn	0+
50Fe	26	24	49.9629880(90)	152.0(6) ms	β+, p?	49Cr	0+
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+
52mFe	6960.7(3) keV			45.9(6) s	IT (0.021%)	52Fe	12+
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 ¹⁶			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 ¹⁷	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−)
65Fe	26	39	64.9450153(55)	805(10) ms	β−, n?	64Co	(1/2−)
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+
66Fe	26	40	65.9462500(44)	467(29) ms	β−, n?	65Co	0+
67Fe	26	41	66.9509300(41)	394(9) ms	β−	67Co	(1/2-)
67Fe	26	41	66.9509300(41)	394(9) ms	β−, n?	66Co	(1/2-)
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+
68Fe	26	42	67.95288(21)#	188(4) ms	β−, n?	67Co	0+
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+
70Fe	26	44	69.96040(32)#	61.4(7) ms	β−, n?	69Co	0+
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+
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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).¹⁸

Iron-56

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-62.¹⁹ 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 of 56Fe represents the point where further nuclear reactions become energetically unfavorable. Therefore 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

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.²⁰ The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound–Rebka experiment.²¹

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.²² ²³ Iron-58 is also an assisting reagent in the synthesis of superheavy elements.²⁴

Iron-60

Iron-60 has a half-life of 2.6 million years,²⁵ ²⁶ 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 from the decay of 60Fe contributed, together with the energy from the decay of the radionuclide 26Al, to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni in extraterrestrial material may also provide further insight into the origin of the Solar System and its early history.

Iron-60 found in fossilized bacteria in sea floor sediments suggest there was a supernova near the Solar System about 2 million years ago.²⁷ ²⁸ Iron-60 is also found in sediments from 8 million years ago.²⁹ In 2019, researchers found interstellar 60Fe in Antarctica, which they relate to the Local Interstellar Cloud.³⁰

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 (πR2Earth) as it passes through the expanding debris. Where Mej is the mass of ejected material. M Fraction intercepted = π R Earth 2 4 π r 2 M e j {\displaystyle M_{\text{Fraction intercepted }}={\frac {\pi R_{\text{Earth }}^{2}}{4\pi r^{2}}}M_{ej}} 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: Σ e j = M Fraction intercepted A surface,Earth = M e j 16 π r 2 {\displaystyle \Sigma _{ej}={\frac {M_{\text{Fraction intercepted }}}{A_{\text{surface,Earth }}}}={\frac {M_{ej}}{16\pi r^{2}}}} 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. N 60 = ( M e j , 60 / m 60 16 π r 2 ) {\displaystyle N_{60}=\left({\frac {M_{ej,60}/m_{60}}{16\pi r^{2}}}\right)} The equation for N60 can be rearranged to find the distance to the supernova. r = M e j , 60 16 π m 60 N 60 {\displaystyle r={\sqrt {\frac {M_{ej,60}}{16\pi m_{60}N_{60}}}}} 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 (10-5 M☉). r = 10 − 5 M ⊙ 16 π ( 60 m p ) N 60 {\displaystyle r={\sqrt {\frac {10^{-5}M_{\odot }}{16\pi \left(60m_{p}\right)N_{60}}}}} r = 3 × 10 18 m = 100 p c {\displaystyle r=3\times 10^{18}m=100pc} More sophisticated analyses have been reported that take into consideration the flux and deposition of 60Fe as well as possible interfering background sources.³¹

Cobalt-60, the decay product of iron-60, emits 1.173 MeV and 1.332 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.³² ³³

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.

References

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. /wiki/Bibcode_(identifier) ↩
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. /wiki/Mass_Spectrometry_Reviews ↩
mFe – Excited nuclear isomer. /wiki/Nuclear_isomer ↩
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. /wiki/Doi_(identifier) ↩
( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits. ↩
# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS). ↩
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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩
# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩
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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩
Modes of decay: EC:Electron captureIT:Isomeric transitionn:Neutron emissionp:Proton emission /wiki/Electron_capture ↩
Bold symbol as daughter – Daughter product is stable. ↩
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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩
( ) spin value – Indicates spin with weak assignment arguments. ↩
# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN). ↩
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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf ↩
Believed to decay by β+β+ to 54Cr with a half-life of over 4.4×1020 a[4] /wiki/Annum ↩
Lowest mass per nucleon of all nuclides; End product of stellar nucleosynthesis /wiki/Nucleosynthesis ↩
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. /wiki/Bibcode_(identifier) ↩
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. https://ui.adsabs.harvard.edu/abs/1995AmJPh..63..653F/abstract ↩
R. Nave. "Mossbauer Effect in Iron-57". HyperPhysics. Georgia State University. Retrieved 2009-10-13. http://hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear/mossfe.html ↩
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List of isotopes

Iron-54

Iron-56

Iron-57

Iron-58

Iron-60

Further reading

References