Nickel-62

Nickel-62

General
Symbol	62Ni
Names	nickel-62
Protons (Z)	28
Neutrons (N)	34
Nuclide data
Natural abundance	3.6346%
Half-life (t1/2)	Stable
Isotope mass	61.928345 [1] Da
Spin	0
Binding energy	8794.553±0.007 keV
Isotopes of nickel Complete table of nuclides

Nickel-62 is a stable isotope of nickel, having 28 protons and 34 neutrons.

It has the highest binding energy per nucleon of any known nuclide (8.7945 MeV). ^{[2] [3]} It is often stated that ⁵⁶Fe is the "most stable nucleus", and that is correct, but because ⁵⁶Fe has the lowest mass per nucleon, not binding energy per nucleon, of all nuclides. The lower mass per nucleon of ⁵⁶Fe is possible because ⁵⁶Fe has 26/56 ≈ 46.43% protons, while ⁶²Ni has only 28/62 ≈ 45.16% protons. Protons are less massive than neutrons, meaning that the larger fraction of protons in ⁵⁶Fe lowers its mean mass per nucleon without changing its binding energy, which is by definition measured with respect to the actual mix of protons and neutrons in the nucleus (even though free neutrons are unstable. In other words, nickel-62 can be said to have the 'least massive' protons and neutrons of any isotope.

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,^{[ dubious – discuss ]} 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 ⁵⁸Fe and ⁵⁶Fe, with binding energies per nucleon of 8.7922 MeV and 8.7903 MeV, respectively. ^[4]

As noted above, the isotope ⁵⁶Fe has the lowest mass per nucleon of any nuclide, 930.412 MeV/c², followed by ⁶²Ni with 930.417 MeV/c² and ⁶⁰Ni with 930.420 MeV/c². This does not contradict the binding energy numbers because ⁶²Ni has a greater proportion of neutrons which are more massive than protons.

The misconception of ⁵⁶Fe's higher nuclear binding energy probably originated from astrophysics. ^[5] 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 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".

See also

• Isotopes of nickel

References

1. 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.
2. "The Most Tightly Bound Nuclei". hyperphysics.phy-astr.gsu.edu. Retrieved October 23, 2019.
3. Sree Harsha, N. R. (2018). "The tightly bound nuclei in the liquid drop model". European Journal of Physics. 39 (3): 035802. arXiv: 1709.01386 . Bibcode:2018EJPh...39c5802S. doi:10.1088/1361-6404/aaa345. S2CID   250846252.
4. WWW Table of Atomic Masses. Archived 2010-11-24 at the Wayback Machine G. Audi, A.H. Wapstra and C. Thibault (2003). Nuclear Physics A, 729, p. 337.
5. Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics. 63 (7): 653–658. Bibcode:1995AmJPh..63..653F. doi:10.1119/1.17828.