Fusion cycle of the Sun
The cycle starts with the thermal collision of two protons (1H + 1H) to form a deuteron (2H), with the simultaneous creation of a positron (e+) and a neutrino (v). The positron very quickly encounters a free electron (e-) in the sun and both particles annihilate, their mass energy appearing as two gamma-ray photons. Once the deuteron has been produced, it quickly collides with another proton and forms a 3He nucleus and a gamma ray. Two such 3He nuclei may eventually (within ten thousand years) find each other, as the bottom row shows.
Overall, this amounts to the combination of four protons and two electrons to form an alpha particle (4He), two neutrinos, and six gamma rays. Thus, the overall equation is
.