Isotopes of iron

Template:Short description Template:Infobox iron isotopes Natural iron (Template:SubFe) consists of four stable isotopes: 5.845% Template:SupFe (possibly radioactive with half-life >Template:Val years), 91.754% Template:SupFe, 2.119% Template:SupFe and 0.286% Template:SupFe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are Template:SupFe (half-life 2.6 million years) and Template:SupFe (half-life 2.7 years).

Much of the past work on measuring the isotopic composition of iron has centered on determining Template:SupFe 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.

List of isotopes

Template:Isotopes table |-id=Iron-45 | rowspan=4|⁴⁵Fe | rowspan=4 style="text-align:right" | 26 | rowspan=4 style="text-align:right" | 19 | rowspan=4|45.01547(30)# | rowspan=4|2.5(2) ms | 2p (70%) | ⁴³Cr | rowspan=4|3/2+# | rowspan=4| | rowspan=4| |- | β⁺, p (18.9%) | ⁴⁴Cr |- | β⁺, 2p (7.8%) | ⁴³V |- | β⁺ (3.3%) | ⁴⁵Mn |-id=Iron-46 | rowspan=3|⁴⁶Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 20 | rowspan=3|46.00130(32)# | rowspan=3|13.0(20) ms | β⁺, p (78.7%) | ⁴⁵Cr | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁺ (21.3%) | ⁴⁶Mn |- | β⁺, 2p? | ⁴⁴V |-id=Iron-47 | rowspan=2|⁴⁷Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 21 | rowspan=2|46.99235(54)# | rowspan=2|21.9(2) ms | β⁺, p (88.4%) | ⁴⁶Cr | rowspan=2|7/2−# | rowspan=2| | rowspan=2| |- | β⁺ (11.6%) | ⁴⁷Mn |-id=Iron-48 | rowspan=2|⁴⁸Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 22 | rowspan=2|47.980667(99) | rowspan=2|45.3(6) ms | β⁺ (84.7%) | ⁴⁸Mn | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁺, p (15.3%) | ⁴⁷Cr |-id=Iron-49 | rowspan=2|⁴⁹Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 23 | rowspan=2|48.973429(26) | rowspan=2|64.7(3) ms | β⁺, p (56.7%) | ⁴⁸Cr | rowspan=2|(7/2−) | rowspan=2| | rowspan=2| |- | β⁺ (43.3%) | ⁴⁹Mn |-id=Iron-50 | rowspan=2|⁵⁰Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 24 | rowspan=2|49.9629880(90) | rowspan=2|152.0(6) ms | β⁺ | ⁵⁰Mn | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁺, p? | ⁴⁹Cr |-id=Iron-51 | ⁵¹Fe | style="text-align:right" | 26 | style="text-align:right" | 25 | 50.9568551(15) | 305.4(23) ms | β⁺ | ⁵¹Mn | 5/2− | | |-id=Iron-52 | ⁵²Fe | style="text-align:right" | 26 | style="text-align:right" | 26 | 51.94811336(19) | 8.275(8) h | β⁺ | ⁵²Mn | 0+ | | |-id=Iron-52m | rowspan=2 style="text-indent:1em" | ^52mFe | rowspan=2 colspan="3" style="text-indent:2em" | 6960.7(3) keV | rowspan=2|45.9(6) s | β⁺ (99.98%) | ⁵²Mn | rowspan=2|12+ | rowspan=2| | rowspan=2| |- | IT (0.021%) | ⁵²Fe |-id=Iron-53 | ⁵³Fe | style="text-align:right" | 26 | style="text-align:right" | 27 | 52.9453056(18) | 8.51(2) min | β⁺ | ⁵³Mn | 7/2− | | |-id=Iron-53m | style="text-indent:1em" | ^53mFe | colspan="3" style="text-indent:2em" | 3040.4(3) keV | 2.54(2) min | IT | ⁵³Fe | 19/2− | | |- | ⁵⁴Fe | style="text-align:right" | 26 | style="text-align:right" | 28 | 53.93960819(37) | colspan=3 align=center|Observationally StableTemplate:Refn | 0+ | 0.05845(105) | |-id=Iron-54m | style="text-indent:1em" | ^54mFe | colspan="3" style="text-indent:2em" | 6527.1(11) keV | 364(7) ns | IT | ⁵⁴Fe | 10+ | | |- | ⁵⁵Fe | style="text-align:right" | 26 | style="text-align:right" | 29 | 54.93829116(33) | 2.7562(4) y | EC | ⁵⁵Mn | 3/2− | | |- | ⁵⁶Fe | style="text-align:right" | 26 | style="text-align:right" | 30 | 55.93493554(29) | colspan=3 align=center|Stable | 0+ | 0.91754(106) | |- | ⁵⁷Fe | style="text-align:right" | 26 | style="text-align:right" | 31 | 56.93539195(29) | colspan=3 align=center|Stable | 1/2− | 0.02119(29) | |- | ⁵⁸Fe | style="text-align:right" | 26 | style="text-align:right" | 32 | 57.93327358(34) | colspan=3 align=center|Stable | 0+ | 0.00282(12) | |-id=Iron-59 | ⁵⁹Fe | style="text-align:right" | 26 | style="text-align:right" | 33 | 58.93487349(35) | 44.500(12) d | β⁻ | ⁵⁹Co | 3/2− | | |- | ⁶⁰Fe | style="text-align:right" | 26 | style="text-align:right" | 34 | 59.9340702(37) | 2.62(4)×10⁶ y | β⁻ | ⁶⁰Co | 0+ | trace | |-id=Iron-61 | ⁶¹Fe | style="text-align:right" | 26 | style="text-align:right" | 35 | 60.9367462(28) | 5.98(6) min | β⁻ | ⁶¹Co | (3/2−) | | |-id=Iron-61m | style="text-indent:1em" | ^61mFe | colspan="3" style="text-indent:2em" | 861.67(11) keV | 238(5) ns | IT | ⁶¹Fe | 9/2+ | | |-id=Iron-62 | ⁶²Fe | style="text-align:right" | 26 | style="text-align:right" | 36 | 61.9367918(30) | 68(2) s | β⁻ | ⁶²Co | 0+ | | |-id=Iron-63 | ⁶³Fe | style="text-align:right" | 26 | style="text-align:right" | 37 | 62.9402727(46) | 6.1(6) s | β⁻ | ⁶³Co | (5/2−) | | |-id=Iron-64 | ⁶⁴Fe | style="text-align:right" | 26 | style="text-align:right" | 38 | 63.9409878(54) | 2.0(2) s | β⁻ | ⁶⁴Co | 0+ | | |-id=Iron-65 | rowspan=2|⁶⁵Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 39 | rowspan=2|64.9450153(55) | rowspan=2|805(10) ms | β⁻ | ⁶⁵Co | rowspan=2|(1/2−) | rowspan=2| | rowspan=2| |- | β⁻, n? | ⁶⁴Co |-id=Iron-65m1 | style="text-indent:1em" | ^65m1Fe | colspan="3" style="text-indent:2em" | 393.7(2) keV | 1.12(15) s | β⁻? | ⁶⁵Co | (9/2+) | | |-id=Iron-65m2 | style="text-indent:1em" | ^65m2Fe | colspan="3" style="text-indent:2em" | 397.6(2) keV | 418(12) ns | IT | ⁶⁵Fe | (5/2+) | | |-id=Iron-66 | rowspan=2|⁶⁶Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 40 | rowspan=2|65.9462500(44) | rowspan=2|467(29) ms | β⁻ | ⁶⁶Co | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁻, n? | ⁶⁵Co |-id=Iron-67 | rowspan=2|⁶⁷Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 41 | rowspan=2|66.9509300(41) | rowspan=2|394(9) ms | β⁻ | ⁶⁷Co | rowspan=2|(1/2-) | rowspan=2| | rowspan=2| |- | β⁻, n? | ⁶⁶Co |-id=Iron-67m1 | style="text-indent:1em" | ^67m1Fe | colspan="3" style="text-indent:2em" | 403(9) keV | 64(17) μs | IT | ⁶⁷Fe | (5/2+,7/2+) | | |-id=Iron-67m2 | style="text-indent:1em" | ^67m2Fe | colspan="3" style="text-indent:2em" | 450(100)# keV | 75(21) μs | IT | ⁶⁷Fe | (9/2+) | | |-id=Iron-68 | rowspan=2|⁶⁸Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 42 | rowspan=2|67.95288(21)# | rowspan=2|188(4) ms | β⁻ | ⁶⁸Co | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁻, n? | ⁶⁷Co |-id=Iron-69 | rowspan=3|⁶⁹Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 43 | rowspan=3|68.95792(22)# | rowspan=3|162(7) ms | β⁻ | ⁶⁹Co | rowspan=3|1/2−# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁶⁸Co |- | β⁻, 2n? | ⁶⁷Co |-id=Iron-70 | rowspan=2|⁷⁰Fe | rowspan=2 style="text-align:right" | 26 | rowspan=2 style="text-align:right" | 44 | rowspan=2|69.96040(32)# | rowspan=2|61.4(7) ms | β⁻ | ⁷⁰Co | rowspan=2|0+ | rowspan=2| | rowspan=2| |- | β⁻, n? | ⁶⁹Co

|-id=Iron-71 | rowspan=3|⁷¹Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 45 | rowspan=3|70.96572(43)# | rowspan=3|34.3(26) ms | β⁻ | ⁷¹Co | rowspan=3|7/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁷⁰Co |- | β⁻, 2n? | ⁶⁹Co |-id=Iron-72 | rowspan=3|⁷²Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 46 | rowspan=3|71.96860(54)# | rowspan=3|17.0(10) ms | β⁻ | ⁷²Co | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁷¹Co |- | β⁻, 2n? | ⁷⁰Co |-id=Iron-73 | rowspan=3|⁷³Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 47 | rowspan=3|72.97425(54)# | rowspan=3|12.9(16) ms | β⁻ | ⁷³Co | rowspan=3|7/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁷²Co |- | β⁻, 2n? | ⁷¹Co |-id=Iron-74 | rowspan=3|⁷⁴Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 48 | rowspan=3|73.97782(54)# | rowspan=3|5(5) ms | β⁻ | ⁷⁴Co | rowspan=3|0+ | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁷³Co |- | β⁻, 2n? | ⁷²Co |-id=Iron-75 | rowspan=3|⁷⁵Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 49 | rowspan=3|74.98422(64)# | rowspan=3|9# ms
[>620 ns] | β⁻? | ⁷⁵Co | rowspan=3|9/2+# | rowspan=3| | rowspan=3| |- | β⁻, n? | ⁷⁴Co |- | β⁻, 2n? | ⁷³Co |-id=Iron-76 | ⁷⁶Fe | style="text-align:right" | 26 | style="text-align:right" | 50 | 75.98863(64)# | 3# ms
[>410 ns] | β⁻? | ⁷⁶Co | 0+ | | Template:Isotopes table/footer

Iron-54

Template:SupFe is observationally stable, but theoretically can decay to Template:SupCr, with a half-life of more than Template:Val years via double electron capture (εε).

Iron-56

Template:Main Template:SupFe is the most abundant isotope of iron. It is also the isotope with the lowest mass per nucleon, 930.412 MeV/cTemplate:Sup, though not the isotope with the highest nuclear binding energy per nucleon, which is nickel-62. However, because of the details of how nucleosynthesis works, Template:SupFe is a more common endpoint of fusion chains inside supernovae, where it is mostly produced as Template:SupNi. Thus, Template:SupNi is more common in the universe, relative to other metals, including Template:SupNi, Template:SupFe and Template:SupNi, all of which have a very high binding energy.

The high nuclear binding energy of Template:SupFe 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 Template:SupNi, which subsequently decays to [[Isotopes of cobalt|Template:SupCo]] and then Template:SupFe.

Iron-57

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

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

Iron-60

Iron-60 has a half-life of 2.6 million years, 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 Template:SupNi, the granddaughter isotope of Template:SupFe, and the abundance of the stable iron isotopes could be found, which is evidence for the existence of Template:SupFe at the time of formation of the Solar System. Possibly the energy from the decay of Template:SupFe contributed, together with the energy from the decay of the radionuclide [[Aluminium-26|Template:SupAl]], to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of Template:SupNi 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. Iron-60 is also found in sediments from 8 million years ago. In 2019, researchers found interstellar Template:SupFe in Antarctica, which they relate to the Local Interstellar Cloud.

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 4πrTemplate:Sup. The fraction of the material intercepted by the Earth is dependent on its cross-sectional area (πRTemplate:SupTemplate:Sub) as it passes through the expanding debris. Where MTemplate:Sub is the mass of ejected material.$$M_{\text{Fraction intercepted }}=\frac{\pi R_{\text{Earth }}^2}{4\pi r^2}{M}_{ej}$$Assuming the intercepted material is distributed uniformly across the surface of the Earth (4πRTemplate:SupTemplate:Sub), the mass surface density (ΣTemplate:Sub) of the supernova ejecta on Earth is: $${\mathrm{\Sigma }}_{ej}=\frac{M_{\text{Fraction intercepted }}}{A_{\text{surface,Earth }}}=\frac{M_{ej}}{16\pi r^2}$$The number of Template:SupFe atoms per unit area found on Earth can be estimated if the typical amount of Template:SupFe ejected from a supernova is known. This can be done by dividing the surface mass density (ΣTemplate:Sub) by the atomic mass of Template:SupFe. $$N_{60}=\left(\frac{M_{ej,60}/m_{60}}{16\pi r^2}\right)$$The equation for NTemplate:Sup can be rearranged to find the distance to the supernova.$$r=\sqrt{\frac{M_{ej,60}}{16\pi m_{60}{N}_{60}}}$$An example calculation for the distance to the supernova point of origin is given below. This calculation uses speculative values for terrestrial Template:SupFe atom surface density (NTemplate:Sub ≈ 4 × 10Template:Sup atoms/mTemplate:Sup) and a rough estimate of the mass of Template:SupFe ejected by a supernova (10Template:Sup MTemplate:Sub). $$r=\sqrt{\frac{10^{-5}{M}_{\odot }}{16\pi \left(60m_p\right)N_{60}}}$$$$r=3\times 10^{18}m=100pc$$More sophisticated analyses have been reported that take into consideration the flux and deposition of Template:SupFe as well as possible interfering background sources.

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 Template:SupFe synthesis is ongoing in our Galaxy, and probing element production in massive stars.

References

Isotope masses from:

• Template:NUBASE 2003

Isotopic compositions and standard atomic masses from:

• Template:CIAAW2003
• Template:CIAAW 2005

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

• Template:NUBASE 2003
• Template:NNDC
• Template:CRC85

Further reading

• Template:Cite book