Oxygen-16 (
16O) is a
stable isotope of oxygen, having 8
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 beh ...
s and 8
protons in its
nucleus. It has a mass of . Oxygen-16 is the most abundant isotope of oxygen and accounts for 99.762% of oxygen's
natural abundance.
The relative and absolute abundance of
16O are high because it is a principal product of
stellar evolution and because it is a
primordial isotope, meaning it can be made by stars that were
initially made exclusively of hydrogen. Most
16O is synthesized at the end of the
helium fusion
The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon.
Triple-alpha process in stars
Helium accumulates in the cores of stars as a result of the proton–pro ...
process in stars; the
triple-alpha process
The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon.
Triple-alpha process in stars
Helium accumulates in the cores of stars as a result of the proton–pro ...
creates
12C, which captures an additional
4He to make
16O. The
neon-burning process creates additional
16O. Oxygen-16 is
doubly magic.
Solid samples (organic and inorganic) for
16O studies are usually stored in silver cups and measured with
pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
and
mass spectrometry.
Researchers need to avoid improper or prolonged storage of the samples for accurate measurements.
Oxygen-16 was originally the standard from which the
atomic masses of all
nuclides
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 ...
were defined, i.e., one
atomic mass unit
The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at ...
was defined as the mass of oxygen-16, though the atomic mass unit has since been redefined relative to
carbon-12.
References
Oxygen-16
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