Nuclear Reactions in the p-p Chain

This is the nuclear fusion process which fuels the sun and other stars which have core temperatures less than 15 million Kelvin. A reaction cycle yields about 25 MeV of energy. The modeling of these reactions is a part of the standard solar model.

Note that both reactions which produce deuterium also produce a neutrino. Measuring the energy output of the sun and comparing it to this model allows us to predict the number of neutrinos that will hit the earth. The fact that early experiments detected only about a third of that number was called the "solar neutrino problem".