Caughlan, Georgeanne R. Department of Physics, Montana State University, Bozeman, Montana.
Hartmann, Dieter H. Department of Physics and Astronomy, Clemson University, Clemson, South Carolina.
Last reviewed:August 2020
- Neutrino emission
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A group of nuclear reactions involving fusion of light nuclei that converts hydrogen into helium. It is believed to be the principal source of energy in main sequence stars of a little more than a solar mass and of less massive stars. Completion of a chain results in the consumption of four protons (hydrogen-1 nuclei, designated 1H), and the production of a helium (4He) nucleus plus two positrons (e+) and two neutrinos (ν). The two positrons are annihilated along with two electrons (e−), and the total energy release is 26.73 MeV. Approximately 0.58 MeV is released as neutrino energy and is not available as thermal energy in a star. The chain can be thought of as the conversion of four hydrogen atoms into a helium atom plus energy in the form of photons or neutrinos, or the kinetic energy of particles. The energy E = 26.73 MeV arises from the mass difference between four hydrogen atoms and the helium atom, and is calculated from the Einstein mass-energy equation E = Δmc2, where Δm is the mass difference and c2 is the square of the velocity of light. Because hydrogen is the fuel consumed in the process, it is referred to as hydrogen burning by means of the proton-proton chain.
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