proton-proton chain |
A set of thermonuclear reactions in which hydrogen nuclei (protons) fuse to form deuterium; these then fuse to form light helium isotopes, releasing more hydrogen nuclei that undergo further fusion with each other and with other nuclei. The main product of the proton-proton chain is He 4, the most common isotope of helium. The proton-proton chain releases large amounts of energy and involves the conversion of protons into neutrons, positrons, and electron neutrinos. The proton-proton chain is the main reaction in most main-sequence stars, including the Sun. See also carbon cycle, triple alpha process.