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| 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 |
| Nuclear binding energy | 545262.286±0.434 keV |
| Isotopes of nickel Complete table of nuclides | |
Nickel-62 is a stableisotope ofnickel, having 28protons and 34neutrons.
It has the highestbinding energy pernucleon of any knownnuclide (8.7945 MeV).[2][3] It is often stated that56
Fe is the "most stable nucleus", but this is because56Fe has the lowestmass per nucleon, not binding energy per nucleon, of all nuclides. The lower mass per nucleon of56Fe is possible because56Fe has 26/56 ≈ 46.43% protons, while62Ni has only 28/62 ≈ 45.16% protons. Protons are less massive than neutrons, meaning that the larger fraction of protons in56Fe 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 thoughfree neutrons are unstable.) In other words, nickel-62 can be said to have the 'least massive' protons and neutrons of any isotope.
The high binding energy of nickel isotopes in general makes nickel an "end product" of many nuclear reactions (includingneutron capture reactions) throughout theuniverse and accounts for the high relative abundance of nickel—although most nickel in space (and possibly produced by supernova explosions) isnickel-58 (the most common isotope) andnickel-60 (the second-most), with theother stable isotopes (nickel-61, nickel-62, andnickel-64) being quite rare. This suggests that most nickel is produced in supernovas in ther-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 tocobalt-56 and then stable iron-56.
The second and third most tightly bound nuclei are those of58Fe and56Fe, with binding energies per nucleon of 8.7922 MeV and 8.7903 MeV, respectively.[4]
As noted above, the isotope56Fe has the lowest mass per nucleon of any nuclide, 930.412 MeV/c2, followed by62Ni with 930.417 MeV/c2 and60Ni with 930.420 MeV/c2. This does not contradict the binding energy numbers because62Ni has a greater proportion of neutrons which are more massive than protons.
The misconception of56Fe's higher nuclear binding energy probably originated from astrophysics.[5] Duringnucleosynthesis in stars the competition betweenphotodisintegration andalpha capturing causes more56Ni to be produced than62Ni (56Fe is produced later in the star's ejection shell as56Ni decays). The56Ni 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 thealpha 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 ofzinc-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 thefuture of an expanding universe without proton decay includesiron stars rather than "nickel stars".