Isotopes of iron

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Naturally occurring iron (Fe) consists of four isotopes: 5.845% of radioactive ⁵⁴Fe (half-life: >3.1×10²² years), 91.754% of stable ⁵⁶Fe, 2.119% of stable ⁵⁷Fe and 0.282% of stable ⁵⁸Fe. ⁶⁰Fe is an extinct radionuclide of long half-life (1.5 million years).

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.^[1]

The isotope ⁵⁶Fe is of particular interest to nuclear scientists. A common misconception is that this isotope represents the most stable nucleus possible, and that it thus would be impossible to perform fission or fusion on ⁵⁶Fe and still liberate energy. This is not true, as both ⁶²Ni and ⁵⁸Fe are more stable, being the most stable nuclei. However, since ⁵⁶Fe is much more easily produced from lighter nuclei in nuclear reactions, it is the endpoint of fusion chains inside extremely massive stars and is therefore common in the universe, relative to other metals.

In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of ⁶⁰Ni, the daughter product 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. Of the stable isotopes, only ⁵⁷Fe has a nuclear spin (−1/2).
Standard atomic mass: 55.845(2) u

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
45Fe	26	19	45.01458(24)#	4.9(15) ms [3.8(+20-8) ms]	3/2+#
46Fe	26	20	46.00081(38)#	9(4) ms [12(+4-3) ms]	0+
47Fe	26	21	46.99289(28)#	21.8(7) ms	7/2-#
48Fe	26	22	47.98050(8)#	44(7) ms	0+
49Fe	26	23	48.97361(16)#	70(3) ms	(7/2-)
50Fe	26	24	49.96299(6)	155(11) ms	0+
51Fe	26	25	50.956820(16)	305(5) ms	5/2-
52Fe	26	26	51.948114(7)	8.275(8) h	0+
52mFe	6.81(13) MeV			45.9(6) s	(12+)#
53Fe	26	27	52.9453079(19)	8.51(2) min	7/2-
53mFe	3040.4(3) keV			2.526(24) min	19/2-
54Fe	26	28	53.9396105(7)	STABLE [>3.1E+22 a]	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) a	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	3/2-
60Fe	26	34	59.934072(4)	1.5(3)E+6 a	0+
61Fe	26	35	60.936745(21)	5.98(6) min	3/2-,5/2-
61mFe	861(3) keV			250(10) ns	9/2+#
62Fe	26	36	61.936767(16)	68(2) s	0+
63Fe	26	37	62.94037(18)	6.1(6) s	(5/2)-
64Fe	26	38	63.9412(3)	2.0(2) s	0+
65Fe	26	39	64.94538(26)	1.3(3) s	1/2-#
65mFe	364(3) keV			430(130) ns	(5/2-)
66Fe	26	40	65.94678(32)	440(40) ms	0+
67Fe	26	41	66.95095(45)	394(9) ms	1/2-#
67mFe	367(3) keV			64(17) µs	(5/2-)
68Fe	26	42	67.95370(75)	187(6) ms	0+
69Fe	26	43	68.95878(54)#	109(9) ms	1/2-#
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+

See also

J.M. Nielsen, "The Radiochemistry of Iron", National Academy of Sciences--National Research Council, 1960

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.

References

• Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
• Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
• Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
  • Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
  • National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
  • David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.

Footnotes

See also

• Iron-56

Isotopes of manganese	Isotopes of iron	Isotopes of cobalt
Index to isotope pages · Table of nuclides

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