Iron-56 (⁵⁶Fe) is the most common

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

. About 91.754% of all iron is iron-56. Of all nuclides, iron-56 has the lowest mass per

nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...

. With 8.8

MeV In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacu ...

binding energy In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...

per nucleon, iron-56 is one of the most tightly bound nuclei.Nuclear Binding Energy
/ref>

Nickel-62 Nickel-62 is an isotope of nickel having 28 protons and 34 neutrons. It is a stable isotope, with the highest binding energy per nucleon of any known nuclide (8.7945 MeV). It is often stated that 56Fe is the "most stable nucleus", but only beca ...

, 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

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

s, which are slightly more massive than protons. (See the

nickel-62 Nickel-62 is an isotope of nickel having 28 protons and 34 neutrons. It is a stable isotope, with the highest binding energy per nucleon of any known nuclide (8.7945 MeV). It is often stated that 56Fe is the "most stable nucleus", but only beca ...

article for more). Light elements undergoing

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...

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 Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

in stars the competition between

photodisintegration Photodisintegration (also called phototransmutation, or a photonuclear reaction) is a nuclear process in which an atomic nucleus absorbs a high-energy gamma ray, enters an excited state, and immediately decays by emitting a subatomic particle. The ...

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 Observations suggest that the Expansion of the universe, expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this futur ...

. Nonetheless, 28 atoms of nickel-62 fusing into 31 atoms of iron-56 releases of energy. As the

Universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...

ages, matter will slowly convert to ever more tightly bound nuclei, approaching ⁵⁶Fe, ultimately leading to the formation of

iron star In astronomy, an iron star is a hypothetical type of compact star. Unrelatedly, the term "iron star" is also used for blue supergiants which have a forest of forbidden FeII lines in their spectra. They are potentially quiescent hot luminous blue ...

s over ≈10¹⁵⁰⁰ years in an expanding universe without proton decay.

References

* {{Isotope, element=iron , lighter= iron-55 , heavier=

iron-57 Naturally occurring iron (26Fe) consists of four stable isotopes: 5.845% of 54Fe (possibly radioactive with a half-life over years), 91.754% of 56Fe, 2.119% of 57Fe and 0.286% of 58Fe. There are 24 known radioactive isotopes, the most stable of w ...

, before= manganese-56
cobalt-56 , after=Stable Isotopes of iron

See also

References