An Etymological Dictionary of Astronomy and Astrophysics
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A neutrino generated in the → Sun. The main source of solar neutrinos is the → proton-proton chain of reactions: 4 × p→ He + 2e⁺ + 2ν_e, in which an energy of +28 MeV is shared between the reaction products. These are called → low-energy neutrinos. There are less important reactions in the Sun yielding a smaller flux of higher energy neutrinos. The solar neutrino flux can be estimated from the → solar luminosity (L), as follows Since there are two neutrinos for each 28 MeV of energy, the neutrino flux at the Earth distance (d) is given by: ν flux = 2Lsun/(28 MeV) × (1/4πd²) = 6 × 10¹⁰ cm^-2 s^-1. See also the → solar neutrino problem.

→ solar; → neutrino; → flux.

A major discrepancy between the flux of neutrinos detected at Earth from the solar core and that predicted by current models of solar nuclear fusion and our understanding of neutrinos themselves. The problem, lasting from the mid-1960s to about 2002, was a considerably lesser detected number of neutrons compared with theoretical predictions. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the → standard model of particle physics, in particular → neutrino oscillation.

→ solar; → neutrino; → problem.

A measure of the flux of neutrinos from the Sun reaching the Earth. 1 SNU is equal to 10^-36 solar neutrinos captured per target atom per second.

→ solar; → neutrino; → unit.