We consider the decay of massive neutrinos which couple to electrons and are, therefore, produced in nuclear reactors. Lifetime limits for the $\gamma$ and electron-positron decay modes of these neutrinos are deduced from the experimental limit on the singles count rate in the detector used to study neutrino oscillations at the Gösgen reactor. The dominantly coupled neutrinos are light, and their invariant-lifetime limit $\frac{t^{\mathrm{c}.\mathrm{m}.\mathrm{}}}{m_{\nu }}$ is 1-3 sec/eV. The subdominantly coupled heavy neutrinos with mass 1-4 MeV could decay into electron-positron pairs. These pairs were not observed, and from the absence of such a signal we deduce restrictions on the corresponding mixing parameters.

• Received 27 April 1984

DOI:https://doi.org/10.1103/PhysRevD.30.1505