A spectrum of deuterons consistent with the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}+{}_{}{}^3{}_{}{}^{}\mathrm{He}\to {}_{}{}^2{}_{}{}^{}\mathrm{H}+{}_{}{}^4{}_{}{}^{}\mathrm{He}+e^{+}+\nu$ has been detected with a system sensitive to cross sections of 300 pb ${\mathrm{sr}}^{-1\mathrm{}}$ Me${\mathrm{V}}^{-1\mathrm{}}$. The measured cross section is too high for a weak-interaction process: 3.4 nb Me${\mathrm{V}}^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$. It might be due to an interaction of intermediate strength and it could explain the low flux of high-energy solar neutrinos.

• Received 23 December 1974

DOI:https://doi.org/10.1103/PhysRevLett.35.19