Ciao Mohammed,

the nickel-62 have the highest binding energy per nucleon of any known nuclide (8.8 MeV). But the nickel-58 is produced in supernovas in the r-process of neutron capture from nickel-56 immediately after the core-collapse. So, it is the most common isotope and "observationally stable" (that means that are theoretically believed unstable but have not been observed to decay).

This is how I explain it...

Dear B. Mohammed-Azizi many thanks for your very interesting technical question. Although we are inorganic chemists I had never heard about this phenomenon before. As already mentioned by Michele Raucci nickel-62 is the most tightly bound nucleus of all chemical elements. For an interesting article about this please have a look at the following useful links:

The Most Tightly Bound Nuclei

https://xwww.mutah.edu.jo/eijaz/bindingenergymore.htm

and http://hyperphysics.phy-astr.gsu.edu/hbase/NucEne/nucbin2.html#c2

Naturally occurring nickel (Ni) is composed of 5 stable isotopes; 58Ni, 60Ni, 61Ni, 62Ni and 64Ni with 58Ni being the most abundant (68% natural abundance). 18 radioisotopes have been characterized with the most stable being 59Ni with a half-life of 76,000 years, 63Ni with a half-life of 100.1 years, and 56Ni with a half-life of 6.1 days. All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds. This element also has 1 meta state.

Nickel-56 is produced in large quantities in type Ia supernovae and the shape of the light curve of these supernovae corresponds to the decay of nickel-56 to cobalt-56 and then to iron-56.

Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 years. 59Ni has found many applications in isotope geology. 59Ni has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-60 is the daughter product of the extinct radionuclide 60Fe (half-life = 1.5 Myr). Because the extinct radionuclide 60Fe had such a long half-life, its persistence in materials in the solar system at high enough concentrations may have generated observable variations in the isotopic composition of 60Ni. Therefore, the abundance of 60Ni present in extraterrestrial material may provide insight into the origin of the solar system and its early history.

Nickel-62 has the highest binding energy per nucleon of any isotope for any element. Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy.

Nickel-48, discovered in 1999, is the most proton-rich nickel isotope known . With 28 protons and 20 neutrons 48Ni is "doubly magic" (like 208Pb) and therefore unusually stable.

The isotopes of nickel range in atomic weight from 48 u (48-Ni) to 78 u (78-Ni). Nickel-78's half-life was recently measured to be 110 milliseconds and is believed to be an important isotope involved in supernova nucleosynthesis of elements heavier than iron. Standard atomic mass: 58.7(2) u

By comparing the answers of Mr. Michele Raucci with that of Mr. Khaled Ali, I find what seems to me to be an inconsistency.

Indeed Mr Michele Raucci states that nickel 58 comes from Nickel 56 ("manufactured" in the supernova nucleosynthesis) which captures 2 neutrons to become Nickel 58.

On the other hand Mr Khaled Ali, states that Nickel 56 ("made" in the supernova nucleosynthesis) undergoes 2 consecutive beta-plus decays to become Cobalt 56 and then Iron 56 (in the supernova). Looking at Nickel 56, it is indeed beta-plus radioactive ("on earth").

It might be necessary to specify which process has priority in the supernova (i.e. rapid neutron capture or Beta-plus decay?) or in what proportions.

The beginning of the answer to the question asked above can be found at the following URL address:

https://en.wikipedia.org/wiki/Nuclear_binding_energy

The last sentence (in bold) of that text (copied here) seems to provide the right answer to this problem (which seems to me a convincing argument).

At the peak of binding energy, nickel-62 is the most tightly bound nucleus (per nucleon), followed by iron-58 and iron-56.[20] This is the approximate basic reason why iron and nickel are very common metals in planetary cores, since they are produced profusely as end products in supernovae and in the final stages of silicon burning in stars. However, it is not binding energy per nucleon, which controls which exact nuclei are made, because within stars, neutrons are free to convert to protons to release even more energy, per generic nucleon, if the result is a stable nucleus with a larger fraction of protons. In fact, it has been argued that photodisintegration of 62Ni to form 56Fe may be energetically possible in an extremely hot star core, due to this beta decay conversion of neutrons to protons.[21] The conclusion is that at the pressure and temperature conditions in the cores of large stars, energy is released by converting all matter into 56Fe nuclei (ionized atoms). (However, at high temperatures not all matter will be in the lowest energy state.) This energetic maximum should also hold for ambient conditions, say T = 298 K and p = 1 atm, for neutral condensed matter consisting of 56Fe atoms—however, in these conditions nuclei of atoms are inhibited from fusing into the most stable and low energy state of matter. It is generally believed that iron-56 is more common than nickel isotopes in the universe for mechanistic reasons, because its unstable progenitor nickel-56 is copiously made by staged build-up of 14 helium nuclei inside supernovas, where it has no time to decay to iron before being released into the interstellar medium in a matter of a few minutes, as the supernova explodes. However, nickel-56 then decays to cobalt-56 within a few weeks, then this radioisotope finally decays to iron-56 with a half life of about 77.3 days. The radioactive decay-powered light curve of such a process has been observed to happen in type II supernovae, such as SN 1987A. In a star, there are no good ways to create nickel-62 by alpha-addition processes, or else there would presumably be more of this highly stable nuclide in the universe. To understand this, see Nuclear fusion sequence and silicon photodisintegration at the URL:

https://en.wikipedia.org/wiki/Silicon-burning_process#cite_note-5

Explanation in clearer and more concise terms (For those who don't want to dwell on the details)

from: https://en.wikipedia.org/wiki/Silicon-burning_process#cite_note-5

"In stars, rapid nucleosynthesis proceeds by adding helium nuclei (alpha particles) to heavier nuclei. Although nuclei with 58 (iron-58) and 62 (nickel-62) nucleons have the very highest binding energy per nucleon, converting nickel-56 (14 alphas) to the next element, zinc-60 (15 alphas), is a decrease in binding energy per nucleon and actually consumes energy rather than releasing any. Accordingly, Nickel-56 is the last fusion product produced in the core of a high-mass star. Nickel-56 decays into Cobalt-56 and then into Iron-56. This explains the large amount of iron-56 seen in metallic meteorites and the cores of rocky planets." (End of citation)

Conclusion:

So, in spite of their high binding energy and because Nickel-56 is the last fusion product one can conclude that Iron-58, Nickel-58 and Nickel-62 cannot be produced inside stars.

However, the Nickel-58 is produced (in large quantities) in supernovas (end of life of the star) in the rapid-process of neutron capture from Nickel-56 (before it decays) immediately after the core-collapse. Thus, in both "pheneomena" the result is that Nickel-62 is "less produced" than Nickel-58 .

This explain why Nickel-62 (in spite of his highest binding energy compared to the one of Ni-58) is much more less abundant than Nickel-58.

(I hope this explanation is easier to understand in regard to the previous response)

Finally, the interest of this question is to show that an important binding energy for a given nucleus does not always lead to an abundance for this nucleus.

Happy New Year 2022 to all RG colleagues.