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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 in a process called Big Bang nucleosynthesis . [ 1 ]
In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements.
Big Bang nucleosynthesis predicts a primordial abundance of about 25% helium-4 by mass, irrespective of the initial conditions of the universe. As long as the universe was hot enough for protons and neutrons to transform into each other easily, their ratio, determined solely by their relative masses, was about 1 neutron to 7 protons (allowing ...
The x-process in cosmic rays is the primary means of nucleosynthesis for the five stable isotopes of lithium, beryllium, and boron. [3] As the proton–proton chain reaction cannot proceed beyond 4 He due to the unbound nature of 5 He and 5 Li, [ 4 ] and the triple-alpha process skips over all species between 4 He and 12 C, these elements are ...
The slow neutron-capture process, or s-process, is a series of reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars.The s-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron.
Today, nucleosynthesis is widely considered to have taken place in two stages: formation of hydrogen and helium according to the Alpher–Bethe–Gamow theory, and stellar nucleosynthesis of higher elements according to Bethe and Hoyle's later theories.
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Fusing with additional helium nuclei can create heavier elements in a chain of stellar nucleosynthesis known as the alpha process, but these reactions are only significant at higher temperatures and pressures than in cores undergoing the triple-alpha process.