Oxygen-16

Oxygen-16 (symbol: ¹⁶O or ¹⁶
₈O) is a stable isotope of oxygen, with 8 neutrons and 8 protons in its nucleus, and when not ionized, 8 electrons orbiting the nucleus. It is the most abundant isotope of oxygen, accounting for about 99.76% of all oxygen.

Oxygen-16

General
Symbol	16O
Names	oxygen-16
Protons (Z)	8
Neutrons (N)	8
Nuclide data
Natural abundance	99.7621% (SMOW)[1]
Half-life (t1/2)	stable
Isotope mass	15.9949146193[2] Da
Spin	0
Excess energy	−4737.00135(16)[3] keV
Isotopes of oxygen Complete table of nuclides

The relative and absolute abundances of oxygen-16 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 oxygen-16 is synthesized at the end of the helium fusion process in stars; the triple-alpha process creates carbon-12, which captures an additional helium-4 to make oxygen-16. It is also created by the neon-burning process.

Oxygen-16 is doubly magic.

Solid samples (organic and inorganic) for oxygen-16 studies are usually stored in silver cups and measured with pyrolysis and mass spectrometry.^[4] Researchers need to avoid improper or prolonged storage of the samples for accurate measurements.^[4]

Historically, one atomic mass unit was defined as one sixteenth of the mass of an oxygen-16 atom, but has been redefined as one twelfth of the mass of a carbon-12 atom, with the name unified atomic mass unit or dalton.