Experimental Search for a Heavy Neutrino in the Beta Spectrum ofS35

We present results of an experimental study of the shape of the energy spectrum for the decay ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}\to {}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}+e^{-}+{\nu }_e$. The measurements were performed to search for evidence of a beta-decay branch with a heavy neutrino. No evidence for heavy neutrinos is observed. In particular, our limit for the branch to a 17-keV neutrino is 0.4%, in serious disagreement with the 3% branch claimed by Simpson.