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Iron-56 is the most common isotope of iron. About 91.754% of all iron is iron-56.
Of all isotopes, 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 has a higher 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.
Thus, light elements undergoing nuclear fusion and heavy elements undergoing nuclear fission release energy as their nucleons bind more tightly, and the resulting nuclei approach the minimum total energy per nucleon, which occurs at iron-56.
As the Universe ages, more of the matter is converted into extremely tightly bound nuclei, such as iron-56. This progression of matter toward iron and nickel is one of the phenomena responsible for the heat death of the universe. Nevertheless, the production of these elements is in decreasing at the present age of the Universe, after a rapid growth at the beginning of the stellar era. The matter would certainly never be quite entirely converted in such elements.
References
- ^ Nuclear Binding Energy
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