Nickel-62
Encyclopedia
Nickel-62 is an isotope
of nickel
having 28 proton
s and 34 neutron
s.
It is a stable isotope
, with the highest binding energy
per nucleon
of any known nuclide
(8.7945 MeV). It is often stated (e.g. here) that 56Fe
is the "most stable nucleus", but actually 56Fe has the lowest mass per nucleon (not binding energy per nucleon) of all nuclides. This misconception 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 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.
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.
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 is not a contradiction because 62Ni has a greater proportion of neutrons which are more massive than protons.
If one looks only at the nuclei proper, without including the electron cloud, 56Fe has again the lowest mass per nucleon (930.175 MeV/c2), followed by 60Ni (930.181 MeV/c2) and 62Ni (930.187 MeV/c2).
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
having 28 proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and 34 neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s.
It is a stable isotope
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
, with the highest binding energy
Nuclear binding energy
Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts. The component parts are neutrons and protons, which are collectively called nucleons...
per nucleon
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...
of any known nuclide
Nuclide
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state....
(8.7945 MeV). It is often stated (e.g. here) that 56Fe
Iron-56
Iron-56 is the most common isotope of iron. About 91.754% of all iron is iron-56.Of all isotopes, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei....
is the "most stable nucleus", but actually 56Fe has the lowest mass per nucleon (not binding energy per nucleon) of all nuclides. This misconception probably originated from astrophysics. During nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...
in stars the competition between photodisintegration
Photodisintegration
Photodisintegration is a physical process in which an extremely high energy gamma ray interacts with an atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single proton or neutron is effectively knocked out of the nucleus by the...
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 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
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
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
R-process
The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
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.
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.
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 is not a contradiction because 62Ni has a greater proportion of neutrons which are more massive than protons.
If one looks only at the nuclei proper, without including the electron cloud, 56Fe has again the lowest mass per nucleon (930.175 MeV/c2), followed by 60Ni (930.181 MeV/c2) and 62Ni (930.187 MeV/c2).