Astrophysical Constraints on the Radiative Lifetime of Neutrinos with Mass between 10 and 100 eV/c2

Upper limits to astronomical photon backgrounds are used to derive constraints on the radiative lifetime of neutrinos. With the assumption that the radiative decay dominates the decay routes available, comparisons with predicted fluxes exclude radiative lifetimes between ${10}^{13}$ and ${10}^{22}$-${10}^{23}$ sec for neutrinos which decay to lighter neutrinos and 5-50-eV photons. For $m_{{\nu }_L}\ll m_{{\nu }_H}$, this photon-energy range corresponds to a parent-neutrino-mass range of 10-100 eV/${\mathit{c}}^2$.