Naturally occurring

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

(₂₆Fe) consists of four stable

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

s: 5.845% of ⁵⁴Fe (possibly radioactive with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

over years), 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). Much of the past work on measuring the isotopic composition of Fe has centered on determining ⁶⁰Fe variations due to processes accompanying

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

(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 isotope The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...

s of iron. Much of this work has been driven by the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and planetary science communities, although applications to biological and industrial systems are beginning to emerge.

List of isotopes

, - , rowspan=2, ⁴⁵Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 19 , rowspan=2, 45.01458(24)# , rowspan=2, 1.89(49) ms , β⁺ (30%) , ⁴⁵Mn , rowspan=2, 3/2+# , rowspan=2, , rowspan=2, , - , 2 p (70%) , ⁴³Cr , - , rowspan=2, ⁴⁶Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 20 , rowspan=2, 46.00081(38)# , rowspan=2, 9(4) ms
2(+4-3) ms, β⁺ (>99.9%) , ⁴⁶Mn , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺, p (<.1%) , ⁴⁵Cr , - , rowspan=2, ⁴⁷Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 21 , rowspan=2, 46.99289(28)# , rowspan=2, 21.8(7) ms , β⁺ (>99.9%) , ⁴⁷Mn , rowspan=2, 7/2−# , rowspan=2, , rowspan=2, , - , β⁺, p (<.1%) , ⁴⁶Cr , - , rowspan=2, ⁴⁸Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 22 , rowspan=2, 47.98050(8)# , rowspan=2, 44(7) ms , β⁺ (96.41%) , ⁴⁸Mn , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺, p (3.59%) , ⁴⁷Cr , - , rowspan=2, ⁴⁹Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 23 , rowspan=2, 48.97361(16)# , rowspan=2, 70(3) ms , β⁺, p (52%) , ⁴⁸Cr , rowspan=2, (7/2−) , rowspan=2, , rowspan=2, , - , β⁺ (48%) , ⁴⁹Mn , - , rowspan=2, ⁵⁰Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 24 , rowspan=2, 49.96299(6) , rowspan=2, 155(11) ms , β⁺ (>99.9%) , ⁵⁰Mn , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺, p (<.1%) , ⁴⁹Cr , - , ⁵¹Fe , style="text-align:right" , 26 , style="text-align:right" , 25 , 50.956820(16) , 305(5) ms , β⁺ , ⁵¹Mn , 5/2− , , , - , ⁵²Fe , style="text-align:right" , 26 , style="text-align:right" , 26 , 51.948114(7) , 8.275(8) h , β⁺ , ^52mMn , 0+ , , , - , style="text-indent:1em" , ^52mFe , colspan="3" style="text-indent:2em" , 6.81(13) MeV , 45.9(6) s , β⁺ , ⁵²Mn , (12+)# , , , - , ⁵³Fe , style="text-align:right" , 26 , style="text-align:right" , 27 , 52.9453079(19) , 8.51(2) min , β⁺ , ⁵³Mn , 7/2− , , , - , style="text-indent:1em" , ^53mFe , colspan="3" style="text-indent:2em" , 3040.4(3) keV , 2.526(24) min , IT , ⁵³Fe , 19/2− , , , - , ⁵⁴Fe , style="text-align:right" , 26 , style="text-align:right" , 28 , 53.9396090(5) , colspan=3 align=center,

Observationally Stable Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes. Th ...

, 0+ , 0.05845(35) , 0.05837–0.05861 , - , style="text-indent:1em" , ^54mFe , colspan="3" style="text-indent:2em" , 6526.9(6) keV , 364(7) ns , , , 10+ , , , - , ⁵⁵Fe , style="text-align:right" , 26 , style="text-align:right" , 29 , 54.9382934(7) , 2.737(11) y , EC , ⁵⁵Mn , 3/2− , , , - , ⁵⁶FeLowest mass per nucleon of all nuclides; End product of stellar

, style="text-align:right" , 26 , style="text-align:right" , 30 , 55.9349363(5) , colspan=3 align=center, Stable , 0+ , 0.91754(36) , 0.91742–0.91760 , - , ⁵⁷Fe , style="text-align:right" , 26 , style="text-align:right" , 31 , 56.9353928(5) , colspan=3 align=center, Stable , 1/2− , 0.02119(10) , 0.02116–0.02121 , - , ⁵⁸Fe , style="text-align:right" , 26 , style="text-align:right" , 32 , 57.9332744(5) , colspan=3 align=center, Stable , 0+ , 0.00282(4) , 0.00281–0.00282 , - , ⁵⁹Fe , style="text-align:right" , 26 , style="text-align:right" , 33 , 58.9348755(8) , 44.495(9) d , β⁻ , ⁵⁹Co , 3/2− , , , - , ⁶⁰Fe , style="text-align:right" , 26 , style="text-align:right" , 34 , 59.934072(4) , 2.6×10⁶ y , β⁻ , ⁶⁰Co , 0+ , trace , , - , ⁶¹Fe , style="text-align:right" , 26 , style="text-align:right" , 35 , 60.936745(21) , 5.98(6) min , β⁻ , ⁶¹Co , 3/2−,5/2− , , , - , style="text-indent:1em" , ^61mFe , colspan="3" style="text-indent:2em" , 861(3) keV , 250(10) ns , , , 9/2+# , , , - , ⁶²Fe , style="text-align:right" , 26 , style="text-align:right" , 36 , 61.936767(16) , 68(2) s , β⁻ , ⁶²Co , 0+ , , , - , ⁶³Fe , style="text-align:right" , 26 , style="text-align:right" , 37 , 62.94037(18) , 6.1(6) s , β⁻ , ⁶³Co , (5/2)− , , , - , ⁶⁴Fe , style="text-align:right" , 26 , style="text-align:right" , 38 , 63.9412(3) , 2.0(2) s , β⁻ , ⁶⁴Co , 0+ , , , - , ⁶⁵Fe , style="text-align:right" , 26 , style="text-align:right" , 39 , 64.94538(26) , 1.3(3) s , β⁻ , ⁶⁵Co , 1/2−# , , , - , style="text-indent:1em" , ^65mFe , colspan="3" style="text-indent:2em" , 364(3) keV , 430(130) ns , , , (5/2−) , , , - , rowspan=2, ⁶⁶Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 40 , rowspan=2, 65.94678(32) , rowspan=2, 440(40) ms , β⁻ (>99.9%) , ⁶⁶Co , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (<.1%) , ⁶⁵Co , - , rowspan=2, ⁶⁷Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 41 , rowspan=2, 66.95095(45) , rowspan=2, 394(9) ms , β⁻ (>99.9%) , ⁶⁷Co , rowspan=2, 1/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (<.1%) , ⁶⁶Co , - , style="text-indent:1em" , ^67mFe , colspan="3" style="text-indent:2em" , 367(3) keV , 64(17)

µs A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1 ...

, , , (5/2−) , , , - , rowspan=2, ⁶⁸Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 42 , rowspan=2, 67.95370(75) , rowspan=2, 187(6) ms , β⁻ (>99.9%) , ⁶⁸Co , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n , ⁶⁷Co , - , rowspan=2, ⁶⁹Fe , rowspan=2 style="text-align:right" , 26 , rowspan=2 style="text-align:right" , 43 , rowspan=2, 68.95878(54)# , rowspan=2, 109(9) ms , β⁻ (>99.9%) , ⁶⁹Co , rowspan=2, 1/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (<.1%) , ⁶⁸Co , - , ⁷⁰Fe , style="text-align:right" , 26 , style="text-align:right" , 44 , 69.96146(64)# , 94(17) ms , , , 0+ , , , - , ⁷¹Fe , style="text-align:right" , 26 , style="text-align:right" , 45 , 70.96672(86)# , 30# ms
300 ns, , , 7/2+# , , , - , ⁷²Fe , style="text-align:right" , 26 , style="text-align:right" , 46 , 71.96962(86)# , 10# ms
300 ns, , , 0+ , , * 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.

Iron-54

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

Iron-56

The isotope 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 Nickel-62 is an isotope of nickel having 28 protons and 34 neutrons. It is a stable isotope, with the highest binding energy per nucleon of any known nuclide (8.7945 MeV). It is often stated that 56Fe is the "most stable nucleus", but only beca ...

. 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 A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...

, including ⁶²Ni, ⁵⁸Fe and ⁶⁰Ni, all of which have a very high binding energy.

Iron-57

The isotope ⁵⁷Fe is widely used in

Mössbauer spectroscopy Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer (sometimes written "Moessbauer", German: "Mößbauer") in 1958, consists of the nearly recoil-free emission and abs ...

and the related

nuclear resonance vibrational spectroscopy Nuclear resonance vibrational spectroscopy is a synchrotron-based technique that probes vibrational energy levels. The technique, often called NRVS, is specific for samples that contain nuclei that respond to Mössbauer spectroscopy, most commonl ...

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 physics and general relativity, gravitational redshift (known as Einstein shift in older literature) is the phenomenon that electromagnetic waves or photons travelling out of a gravitational well (seem to) lose energy. This loss of energy ...

, in the 1960 Pound-Rebka experiment.

Iron-58

Iron-60

Iron-60 is an iron isotope with 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 In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...

cobalt-60 Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt with a half-life of 5.2713 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisot ...

, 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 ⁶⁰ Ni, the

granddaughter isotope In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps (de ...

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 ⁶⁰ Ni present in extraterrestrial material may also provide further insight into the origin of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

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. Iron-60 is also found in sediments from 8 million years ago. In 2019, researchers found interstellar ⁶⁰Fe in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

, which they relate to the

Local Interstellar Cloud The Local Interstellar Cloud (LIC), also known as the Local Fluff, is an interstellar cloud roughly across, through which the Solar System is moving. This feature overlaps a region around the Sun referred to as the solar neighborhood. It is unk ...

References

Isotope masses from: * Isotopic compositions and standard atomic masses from: * * Half-life, spin, and isomer data selected from: * * *