Nucleosynthesis? New to this tour in physics? Start at THE BIG BANG.
“Between 3 minutes and 20 minutes after the Big Bang
During the photon epoch the temperature of the universe falls to the point where atomic nuclei can begin to form.
Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei in the process of nuclear fusion.
Free neutrons combine with protons to form deuterium. Deuterium rapidly fuses into helium-4.
Nucleosynthesis only lasts for about seventeen minutes, since the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue.
By this time, all neutrons have been incorporated into helium nuclei. This leaves about three times more hydrogen than helium-4 (by mass) and only trace quantities of other nuclei.
In physical cosmology, Big Bang nucleosynthesis (abbreviated BBN, also known as primordial nucleosynthesis) refers to the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe.
Primordial nucleosynthesis is believed by most cosmologists to have taken place between approximately 10 seconds until 20 minutes after the Big Bang, and is calculated to be responsible for the formation of most of the universe’s helium as isotope He-4, along with small amounts of deuterium (H-2 or D), the helium isotope He-3, and a very small amount of the lithium isotope Li-7.
In addition to these stable nuclei, two unstable or radioactive isotopes were also produced: tritium or H-3; and beryllium-7 (Be-7); but these unstable isotopes later decayed into He-3 and Li-7, as above.
Essentially all the elements heavier than Lithium were created much later, by stellar nucleosynthesis in evolving and exploding stars.
Next lecture MATTER DOMINATION.