Natural iron (Fe) consists of four stable isotopes: 5.85% Fe, 91.75% Fe, 2.12% Fe and 0.28% Fe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are Fe (half-life 2.62 million years) and Fe (half-life 2.7562 years).
Much of the past work on measuring the isotopic composition of iron has centered on determining Fe 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.
List of isotopes
|-id=Iron-45 | rowspan=3|45Fe | rowspan=3 style="text-align:right" | 26 | rowspan=3 style="text-align:right" | 19 | rowspan=3|45.01547(30)# | rowspan=3 style="text-align:center" | 1996 | rowspan=3|2.5(2) ms | 2p (70%) | 43Cr | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β+, p (18.9%) | 44Cr |- | β+, 2p (7.8%) | 43V |-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 style="text-align:center" | 1992 | 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 style="text-align:center" | 1992 | 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 style="text-align:center" | 1987 | 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 style="text-align:center" | 1970 | 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 style="text-align:center" | 1977 | 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) | style="text-align:center" | 1972 | 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) | style="text-align:center" | 1948 | 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 style="text-align:center" | 1975 | 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) | style="text-align:center" | 1938 | 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 | style="text-align:center" | 1966 | 2.54(2) min | IT | 53Fe | 19/2−
|-id=Iron-54 | 54Fe | style="text-align:right" | 26 | style="text-align:right" | 28 | 53.93960819(37) | style="text-align:center" | 1924 | colspan=3 align=center|Observationally Stable | 0+ | 0.05845(105) | |-id=Iron-54m | style="text-indent:1em" | 54mFe | colspan="3" style="text-indent:2em" | 6527.1(11) keV | style="text-align:center" | 1978 | 364(7) ns | IT | 54Fe | 10+
|-id=Iron-55 | 55Fe | style="text-align:right" | 26 | style="text-align:right" | 29 | 54.93829116(33) | style="text-align:center" | 1939 | 2.7562(4) y | EC | 55Mn | 3/2−
|-id=Iron-56 | 56FeLowest mass per nucleon of all nuclides; End product of stellar nucleosynthesis | style="text-align:right" | 26 | style="text-align:right" | 30 | 55.93493554(29) | style="text-align:center" | 1922 | colspan=3 align=center|Stable | 0+ | 0.91754(106) | |-id=Iron-57 | 57Fe | style="text-align:right" | 26 | style="text-align:right" | 31 | 56.93539195(29) | style="text-align:center" | 1935 | colspan=3 align=center|Stable | 1/2− | 0.02119(29) | |-id=Iron-58 | 58Fe | style="text-align:right" | 26 | style="text-align:right" | 32 | 57.93327358(34) | style="text-align:center" | 1935 | 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) | style="text-align:center" | 1938 | 44.500(12) d | β− | 59Co | 3/2−
|-id=Iron-60 | 60Fe | style="text-align:right" | 26 | style="text-align:right" | 34 | 59.9340702(37) | style="text-align:center" | 1957 | 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) | style="text-align:center" | 1957 | 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 | style="text-align:center" | 1998 | 238(5) ns | IT | 61Fe | 9/2+
|-id=Iron-62 | 62Fe | style="text-align:right" | 26 | style="text-align:right" | 36 | 61.9367918(30) | style="text-align:center" | 1975 | 68(2) s | β− | 62Co | 0+
|-id=Iron-63 | 63Fe | style="text-align:right" | 26 | style="text-align:right" | 37 | 62.9402727(46) | style="text-align:center" | 1980 | 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) | style="text-align:center" | 1980 | 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 style="text-align:center" | 1985 | 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 | style="text-align:center" | 1999 | 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 | style="text-align:center" | 1998 | 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 style="text-align:center" | 1985 | 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 style="text-align:center" | 1985 | 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 | style="text-align:center" | 1998 | 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 | (2003) | 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 style="text-align:center" | 1985 | 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 style="text-align:center" | 1992 | 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 style="text-align:center" | 1997 | 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 style="text-align:center" | 1997 | 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 style="text-align:center" | 1997 | 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 style="text-align:center" | 2010 | 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 style="text-align:center" | 2010 | 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 style="text-align:center" | 2013 | 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)# | style="text-align:center" | 2017 | 3# ms[>410 ns] | β−? | 76Co | 0+
|-id=Iron-77 | 77Fe | style="text-align:right" | 26 | style="text-align:right" | 51 | | style="text-align:center" | 2026
Iron-56
Fe is the most abundant isotope of iron. It is also the isotope with the lowest mass per nucleon, 930.412 MeV/c, 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, Fe is a more common endpoint of fusion inside supernovae, where it is mostly produced as Ni, which subsequently decays to Co and then iron. Thus, Fe is more common in the universe, relative to other heavy elements, including Ni, Fe, and Ni, all of which have a comparably high binding energy.
Iron-57 Fe 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-60 Iron-60 has a half-life of 2.62 million years, 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 Ni, the granddaughter isotope of Fe, and the abundance of the stable iron isotopes could be found, which is evidence for the existence of Fe at the time of formation of the Solar System. Depending on its original abundance, the energy from the decay of Fe may have been significant, along with that of Al, 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.