It is a stable isotope of oxygen, with 8 neutrons and 8 protons in its nucleus, and when not ionized, 8 electrons orbiting the nucleus.
[2] 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.
Solid samples (organic and inorganic) for oxygen-16 studies are usually stored in silver cups and measured with pyrolysis and mass spectrometry.
[3] Researchers need to avoid improper or prolonged storage of the samples for accurate measurements.