A search for neutrinos of mass 10–40 keV has been made by studying the internal-bremsstrahlung spectrum of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$. We find evidence for a 17.2-keV neutrino with a mixing ratio of 1.6%.

• Received 23 January 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.560