Possible Relation of a Null Solar Neutrino Flux to the II Year Solar Cycle

Abstract

AN experimental measurement of the flux of neutrinos from the Sun has recently been reported¹. The method uses 3.9×10⁵ l. of C₂Cl₄ to absorb neutrinos in the ³⁷Cl(ν,e⁻)³⁷Ar reaction, which has a threshold at 0.81 MeV and is energy-sensitive. Because of the enhanced cross-section for energetic neutrinos, the chief contribution to the counting rate was expected from ⁸B decay in the solar core². But the number of neutrinos detected did not exceed the measured background for the instrument, and so served only to provide an upper limit on the flux of energetic solar neutrinos. The authors concluded that less than 9 per cent of the Sun's energy is produced by the carbon–nitrogen cycle.