Isotopes of iron

Naturally occurring iron (Fe) consists of four stable 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.^[1]

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 (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.^[2] 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.^[3] The transition was famously used to make the first definitive measurement of gravitational redshift, in the 1960 Pound-Rebka experiment.^[4]

Iron-60

Iron-60 is an iron isotope with a half-life of 2.6 million years,^[5][6] but was thought until 2009 to have a half-life of 1.5 million years. It undergoes beta decay to cobalt-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 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.

Remnants of Iron-60 found in fossilised bacteria in sea floor sediments suggest there was a supernova in the vicinity of the solar system approx 2 million years ago.^[7][8]

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)[9][n 1]	daughter isotope(s)[n 2]	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[n 3]			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[n 4]	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)	2.6×10^6 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+

1. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. Bold for stable isotopes
3. Believed to decay by β⁺β⁺ to ⁵⁴Cr with a half-life of over 3.1×10²² a
4. Lowest mass per nucleon of all nuclides; End product of stellar nucleosynthesis

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

1. N. Dauphas; O. Rouxel (2006). "Mass spectrometry and natural variations of iron isotopes". Mass Spectrometry Reviews. 25 (4): 515–550. doi:10.1002/mas.20078. PMID 16463281.
2. Fewell, M. P. "The atomic nuclide with the highest mean binding energy". American Journal of Physics 63 (7): 653-58. Accessed: 2011-03-22. (Archived by WebCite® at http://www.webcitation.org/5xNHry2gq)
3. R. Nave. "Mossbauer Effect in Iron-57". HyperPhysics. Georgia State University. Retrieved 2009-10-13.
4. Pound, R. V.; Rebka Jr. G. A. (April 1, 1960). "Apparent weight of photons". Physical Review Letters. 4 (7): 337–341. Bibcode:1960PhRvL...4..337P. doi:10.1103/PhysRevLett.4.337.
5. Rugel, G.; Faestermann, T.; Knie, K.; Korschinek, G.; Poutivtsev, M.; Schumann, D.; Kivel, N.; Günther-Leopold, I.; Weinreich, R.; Wohlmuther, M. (2009). "New Measurement of the ⁶⁰Fe Half-Life". Physical Review Letters. 103 (7): 72502. Bibcode:2009PhRvL.103g2502R. doi:10.1103/PhysRevLett.103.072502.
6. "Eisen mit langem Atem".
7. Ancient bacteria store signs of supernova smattering
8. Ocean sediment sample holds iron believed to be from a supernova. Aug 2016
9. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. Check date values in: |access-date= (help)
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.
  • "Supernova iron discovered on Earth’s Moon - The Hindu"

Further reading

• J. M. Nielsen (1960). The Radiochemistry of Iron (PDF). National Academy of Sciences/National Research Council.