Using a chemically purified sample of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$ and a coaxial Ge detector, we collected a high-statistics internal-bremsstrahlung photon spectrum, and conducted a local search for departures from a smooth shape near the end point. We find no evidence for emission of a neutrino in the mass range 5–25 keV. In particular, a 17 keV neutrino with ${\sin }^2$θ=0.008 is excluded at the 7σ level.

• Received 13 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.1759