Iron-56
| General | |
|---|---|
| Symbol | 56Fe |
| Names | iron-56 |
| Protons (Z) | 26 |
| Neutrons (N) | 30 |
| Nuclide data | |
| Natural abundance | 91.754%[1] |
| Isotope mass | 55.9349355[2] Da |
| Spin | 0+ |
| Excess energy | −60601.003±1.354 keV |
| Binding energy | 492253.892±1.356 keV |
| Isotopes of iron Complete table of nuclides | |
Iron-56 (56Fe) is one of four stable isotopes of iron, and the most common, comprising about 91.754% of the iron on Earth.
Of all nuclides, iron-56 has the lowest mass per nucleon. With a binding energy of 8.79 MeV per nucleon, iron-56 is one of the most tightly bound nuclei.[3]
The high nuclear binding energy for 56Fe represents the point where further nuclear reactions become energetically unfavorable. Because of this, it is among the heaviest elements formed in stellar nucleosynthesis reactions in massive stars. These reactions fuse lighter elements like magnesium, silicon, and sulfur to form heavier elements. Among the heavier elements formed is 56Ni, which subsequently decays to 56Co and then 56Fe.
Relationship to nickel-62
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 stellar nucleosynthesis 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).
Although nickel-62 has a higher binding energy per nucleon, the conversion of 28 atoms of nickel-62 into 31 atoms of iron-56 releases energy: 5.7 keV per nucleon. As the universe ages, matter will slowly convert to ever more tightly bound nuclei, approaching 56Fe, ultimately leading to the formation of iron stars in, roughly, 101500 years, assuming an expanding universe without proton decay.[4]
See also
- Isotopes of iron
- Iron star
References
- ^ "Standard Atomic Weights: Iron". CIAAW. 2000.
- ^ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3) 030003. doi:10.1088/1674-1137/abddaf.
- ^ "Nuclear Binding Energy". hyperphysics.phy-astr.gsu.edu. Retrieved 2025-05-12.
- ^ 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.