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 actually ⁵⁶Fe merely has the lowest mass per nucleon (not binding energy per nucleon) of all nuclides. The lower mass per nucleon in Fe-56 is enhanced by the fact that ⁵⁶Fe has 26/56 = 46.43% protons, while ⁶²Ni has only 28/62 = 45.16% protons, and the relatively larger fraction of light protons in ⁵⁶Fe lowers its mean mass-per-nucleon ratio in a way that has no effect on its binding energy.

The misconception of ⁵⁶Fe's high nuclear binding energy probably originated from astrophysics. 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). The ⁵⁶Ni is the natural end product of silicon-burning at the end of a supernova's life and is the product of 14 alpha captures in the alpha process which builds more massive elements in steps of 4 nucleons, from carbon. This alpha process in supernovae burning ends here because of the higher energy of zinc-60, which would be produced in the next step, after addition of another "alpha" (or more properly termed, helium nucleus).

The high binding energy of nickel isotopes in general makes nickel an "end product" of many nuclear reactions (including neutron capture reactions) throughout the universe and accounts for the high relative abundance of nickel—although most of the nickel in space (and thus produced by supernova explosions) is nickel-58 (the most common isotope) and nickel-60 (the second-most, with the other stable isotopes (nickel-61, nickel-62, and nickel-64) being quite rare). This suggests that most nickel is produced in supernovas in the r-process of neutron capture by nickel-56 immediately after the core-collapse, with any nickel-56 that escapes the supernova explosion rapidly decaying to cobalt-56 and then stable iron-56.

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