Animation of the proton-proton II chain reaction, one of the nuclear reactions that powers the Sun by converting hydrogen to helium. In the Sun's core, it is hot and dense enough that protons (red) can collide and fuse, forming a diproton. One proton then undergoes beta decay, turning into a neutron (yellow) and emitting a positron (pink) and a neutrino (orange star), forming a deuterium nucleus (hydrogen-2). Another proton then fuses with this, forming helium-3 and emitting a gamma ray (yellow wave). This then collides with a helium-4 nucleus, forming beryllium-7 and another gamma ray. An electron then impacts this nucleus, forming lithium-7 and emitting another neutrino, before another proton collides, forming beryllium-8, which then splits into two helium-4 nuclei. This p-p II branch produces 0.11% of the Sun's energy. See clips K003 3971 for the dominant pp I branch, K003 4581 for the pp III branch, and K003 4574 for the very rare pp IV branch.