Nickel-62

Properties

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 nickel in space (and possibly 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 from 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.

Relationship to iron-56

The second and third most tightly bound nuclei are those of Fe and Fe, with binding energies per nucleon of 8.7922 MeV and 8.7903 MeV, respectively.

As noted above, the isotope Fe has the lowest mass per nucleon of any nuclide, 930.412 MeV/c, followed by Ni with 930.417 MeV/c and Ni with 930.420 MeV/c. This does not contradict the binding energy numbers because Ni has a greater proportion of neutrons which are more massive than protons.

The misconception of Fe's higher nuclear binding energy probably originated from astrophysics. During nucleosynthesis in stars the competition between photodisintegration and alpha capturing causes more Ni to be produced than Ni (Fe is produced later in the star's ejection shell as Ni decays). The Ni 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 supernovas burning ends here because of the production of zinc-60, which would be the next step after addition of another "alpha", is unfavorable.

Nonetheless, 28 atoms of nickel-62 fusing into 31 atoms of iron-56 releases 5.7 keV per nucleon; hence the future of an expanding universe without proton decay includes iron stars rather than "nickel stars".

References

References

1. {{AME2020 II
2. "The Most Tightly Bound Nuclei".
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4. [http://ie.lbl.gov/toi2003/MassSearch.asp WWW Table of Atomic Masses.] {{webarchive. link. (2010-11-24 G. Audi, A.H. Wapstra and C. Thibault (2003). ''Nuclear Physics A'', 729, p. 337.)
5. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics.