= Proton-proton chain branches
{title2=pp I, pp II, pp III}
The <proton–proton chain> first produces deuterium by a weak reaction and then helium-3 by proton capture. pp I ends with ${}^3\mathrm{He}+{}^3\mathrm{He}\to{}^4\mathrm{He}+2p$. pp II passes through beryllium-7 <electron capture> to lithium-7 and then proton capture. pp III passes through boron-8 <beta-plus decay> and beryllium-8 breakup. Each branch produces one net helium-4 nucleus from four protons, but the <neutrino> spectrum and deposited heat differ. In pp II the net weak reactions involve one emitted positron and one captured electron.
Back to article page
