Isotopes of iron

Naturally occurring iron (Fe) consists of four isotopes: 5.845% of ⁵⁴Fe (possibly radioactive with a half-life over 3.1×10²² years), 91.754% of ⁵⁶Fe, 2.119% of ⁵⁷Fe and 0.282% of ⁵⁸Fe. There are 24 known radioactive isotopes and their half-lives are shown below. See Brookhaven National Laboratory Interactive Table of Nuclides for a more accurate reading.

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.

Relative atomic mass: 55.845(2).

Iron-54

⁵⁴Fe is observationally stable, but theoretically can decay to ⁵⁴Cr, with a half-life of more than 3.1x10²² years via double electron capture (2β⁺).

Iron-56

Main article: 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. 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

The isotope 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.

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 to cobalt-60.

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.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
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	53.9396105(7)	Observationally Stable			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	26	30	55.9349375(7)	Stable			0+	0.91754(36)	0.91742–0.91760
57Fe	26	31	56.9353940(7)	Stable			1/2−	0.02119(10)	0.02116–0.02121
58Fe	26	32	57.9332756(8)	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)	2.6×106 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+

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.
• Nuclide masses are given by IUPAP Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO)
• Isotope abundances are given by IUPAC Commission on Isotopic Abundances and Atomic Weights

See also

• Iron-56

References

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Further reading

Isotopes of manganese	Isotopes of iron	Isotopes of cobalt
Table of nuclides