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Iron-56, 56Fe
Namesiron-56, 56Fe, Fe-56
Protons (Z)26
Neutrons (N)30
Nuclide data
Natural abundance91.754%
Isotope mass55.9349375(7) Da
Excess energy−60601.003±1.354 keV
Binding energy492253.892±1.356 keV
Isotopes of iron
Complete table of nuclides
Nuclear binding energy per 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 common isotope of iron. About 91.754% of all iron is iron-56.

Of all nuclides, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei.[1]

Nickel-62, a relatively rare isotope of nickel, has a higher nuclear binding energy per nucleon; this is consistent with having a higher mass-per-nucleon because nickel-62 has a greater proportion of neutrons, which are slightly more massive than protons. (See the nickel-62 article for more). Light elements undergoing nuclear fusion and heavy elements undergoing nuclear fission release energy as their nucleons bind more tightly, so 62Ni might be expected to be common. However, during nucleosynthesis in stars the competition between photodisintegration and alpha capturing causes more 56Ni to be produced than 62Ni (56Fe is produced later in the star's ejection shell as 56Ni decays).

Production of these elements has decreased considerably from what it was at the beginning of the stelliferous era.[citation needed]

Nonetheless, 28 atoms of nickel-62 fusing into 31 atoms of iron-56 releases 0.011 u of energy. As the Universe ages, matter will slowly convert to ever more tightly bound nuclei, approaching 56Fe, ultimately leading to the formation of iron stars over ≈101500 years in an expanding universe without proton decay.[2]

See also[edit]


  1. ^ Nuclear Binding Energy
  2. ^ Dyson, Freeman J. (1979). "Time without end: Physics and biology in an open universe". Reviews of Modern Physics. 51 (3): 447–460. Bibcode:1979RvMP...51..447D. doi:10.1103/RevModPhys.51.447.
Iron-56 is an
isotope of iron
Decay product of:
Decay chain
of iron-56
Decays to: