Completion of the Proton-Proton Reaction Chain and the Possibility of Energetic Neutrino Emission by Hot Stars.

Abstract

The relatively large value for the cross-section of the He3(α,γ)Be7 reaction found experimentally by Holmgren and Johnston (1958) indicates that this reaction will complete the proton-proton reaction chain in stars which contain helium in comparable amounts to hydrogen and which operate at effective temperatures in excess of 13 × 106 degrees. Modifications to the rates of helium production and of energy generation by the proton-proton chain given by Burbidge, Burbidge, Fowler, and Hoyle (1957) are necessitated by this mode of completion of the chain. Correction factors have been calculated for several values of x He/x H over an appropriate range of temperatures. The Be7 produced is consumed by electron capture and by proton capture, and an estimate of the relative rates of these two processes is discussed. In hot stars operating at > 20 × 106 degrees, the proton capture forming B8 will probably predominate, and the B8 decay will result in the emission of energetic neutrinos up to 14.1 Mev in energy. If the proton-capture cross-section for Be7 is relatively large, it may even be that a substantial flux of such neutrinos is emitted by the sun. The flux at the earth will be at most ~2 × 10+10 neutrinos/cm2 sec. If the flux is not too small compared to this maximum value, it may be detectable through observations on Cl37 (v,β−)A37, using the techniques developed by Davis (1955).