Iron-56

Iron-56,⁵⁶Fe

General
Symbol	56Fe
Names	iron-56, 56Fe, Fe-56
Protons(Z)	26
Neutrons(N)	30
Nuclide data
Natural abundance	91.754%
Isotope mass	55.9349375(7)Da
Spin	0+
Excess energy	−60601.003±1.354keV
Binding energy	492253.892±1.356keV
Isotopes of iron Complete table of nuclides

Nuclear binding energyper nucleon of common isotopes; iron-56 labelled at the curve's crest. The rarer isotopes nickel-62 and iron-58, which both have higher binding energies, are not shown.

Iron-56(⁵⁶Fe) is the most commonisotopeofiron.About 91.754% of all iron is iron-56.

Of allnuclides,iron-56 has the lowest mass pernucleon.With 8.8MeVbinding energyper nucleon, iron-56 is one of the most tightly bound nuclei.

The high nuclear binding energy for⁵⁶Fe represents the point where further nuclear reactions become energetically unfavorable. Because of this, it is among the heaviest elements formed instellar nucleosynthesisreactions in massive stars. These reactions fuse lighter elements like magnesium, silicon, and sulfur to form heavier elements. Among the heavier elements formed is⁵⁶Ni,which subsequently decays to⁵⁶Coand then⁵⁶Fe.

Relationship to nickel-62

Nickel-62,a relatively rare isotope of nickel, has a highernuclear binding energyper nucleon; this is consistent with having a higher mass-per-nucleon because nickel-62 has a greater proportion ofneutrons,which are slightly more massive thanprotons.(See thenickel-62article for more). Light elements undergoingnuclear fusionand heavy elements undergoingnuclear fissionrelease energy as their nucleons bind more tightly, so⁶²Ni might be expected to be common. However, duringstellar nucleosynthesisthe competition betweenphotodisintegrationandAlpha capturingcauses more⁵⁶Nito be produced than⁶²Ni (⁵⁶Fe is produced later in the star's ejection shell as⁵⁶Ni decays).

Although nickel-62 has a higher binding energy per nucleon, the conversion of 28 atoms of nickel-62 into 31 atoms of iron-56 releases0.011Daof energy. As theuniverseages, matter will slowly convert to ever more tightly bound nuclei, approaching⁵⁶Fe, ultimately leading to the formation ofiron starsover ≈ 10¹⁵⁰⁰years, assuming anexpanding universe without proton decay.

See also

• Isotopes of iron
• Iron star

References

• de Laeter, John Robert;Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003)."Atomic weights of the elements. Review 2000 (IUPAC Technical Report)".Pure and Applied Chemistry.75(6): 683–800.doi:10.1351/pac200375060683.