Nickel-62 is an
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers ...
of
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
having 28
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mas ...
s and 34
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beha ...
s.
It is a
stable isotope, with the highest
binding energy
In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...
per
nucleon
In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number).
Until the 1960s, nucleons were ...
of any known
nuclide
A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state.
The word ''nuclide'' was coined by Truman ...
(8.7945 MeV). It is often stated that
56Fe is the "most stable nucleus", but only 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; and the larger fraction of lighter protons in
56Fe lowers its mean mass-per-nucleon ratio in a way that has no effect on its binding energy.
Properties
The high binding energy of nickel isotopes in general makes nickel an "end product" of many nuclear reactions (including
neutron capture
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
reactions) throughout the
universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. A ...
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
Naturally occurring nickel (28Ni) is composed of five stable isotopes; , , , and , with being the most abundant (68.077% natural abundance). 26 radioisotopes have been characterised with the most stable being with a half-life of 76,000 years, ...
(the most common isotope) and
nickel-60 (the second-most), with the
other stable isotopes (
nickel-61
Naturally occurring nickel (28Ni) is composed of five stable isotopes; , , , and , with being the most abundant (68.077% natural abundance). 26 radioisotopes have been characterised with the most stable being with a half-life of 76,000 years, ...
, nickel-62, and
nickel-64) being quite rare. This suggests that most nickel is produced in supernovas in the
r-process
In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", ...
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
Naturally occurring cobalt (Co) consists of a single stable isotope, Co. Twenty-eight radioisotopes have been characterized; the most stable are Co with a half-life of 5.2714 years, Co (271.8 days), Co (77.27 days), and Co (70.86 days). All other ...
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.
As noted above, the isotope
56Fe has the lowest mass per nucleon of any nuclide, 930.412 MeV/c
2, followed by
62Ni with 930.417 MeV/c
2 and
60Ni with 930.420 MeV/c
2. As noted, this does not contradict binding numbers 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 again shows the lowest mass per nucleon (930.175 MeV/c
2), followed by
60Ni (930.181 MeV/c
2), and
62Ni (930.187 MeV/c
2).
The misconception of
56Fe's higher nuclear binding energy probably originated from astrophysics.
During
nucleosynthesis
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions i ...
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
The alpha process, also known as the alpha ladder, is one of two classes of nuclear fusion reactions by which stars convert helium into heavier elements, the other being the triple-alpha process.
The triple-alpha process consumes only helium, ...
which builds more massive elements in steps of 4 nucleons, from carbon. This alpha process in supernovas burning ends here because of the higher energy of
zinc-60, which would be produced in the next step, after addition of another "
alpha
Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , w ...
" (or more properly termed, helium nucleus).
Nonetheless, 28 atoms of nickel-62 fusing into 31 atoms of iron-56 releases of energy; hence the
future of an expanding universe without proton decay includes
iron stars rather than "nickel stars".
See also
*
Isotopes of nickel
Naturally occurring nickel (28Ni) is composed of five stable isotopes; , , , and , with being the most abundant (68.077% natural abundance). 26 radioisotopes have been characterised with the most stable being with a half-life of 76,000 years, ...
References
{{reflist
Isotopes of nickel