Search for admixture of heavy neutrinos with masses between 5 and 55 keV

Using a magnetic spectrometer at a momentum resolution of 0.3%, we have studied the beta spectrum from ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}$. We do not see evidence for the admixture of a heavy neutrino to the usual light (m≃0) ν${̃}_{\mathrm{e}}$ accompanying beta decay, in the mass range between 5 and 50 keV, with a limit for the mixing strength of ‖U${\Vert }^2$<3×${10}^{\mathrm{-}3}$ (90% confidence limit).