  It has been recently shown that excess events observed by the LSND and
MiniBooNE neutrino experiments could be interpreted as a signal from the
radiative decay of a heavy sterile neutrino \nu_h produced in \nu_\mu neutral
current-like interactions. If the \nu_h exist, it would be also produced by the
\nu_\mu beam from the CERN SPS in the neutrino beam line shielding. The \nu_h's
would penetrate the shielding and be observed through the decay \nu_h -> \nu
\gamma, followed by the photon conversion into e+e- pair in the active target
of the NOMAD detector. The \nu_h's could be also produced in the iron of the
magnetic spectrometer of the CHORUS detector, located just in front of NOMAD.
Considering these two sources of \nu_h's we set new constraints on \nu_h
properties and exclude part of the LSND/MiniBooNE \nu_h parameter space using
bounds on single photons production in neutrino reactions recently reported by
the NOMAD collaboration. We find that broad bands in the parameter space are
still open for more sensitive searches for the \nu_h in future neutrino
experiments.
