  We calculate the yield of high energy neutrinos produced in astrophysical
sources with negligible magnetic fields varying their interaction depth from
nearly transparent to opaque. We take into account the scattering of
secondaries on background photons as well as the direct production of neutrinos
in decays of charm mesons. If multiple scattering of nucleons becomes
important, the neutrino spectra from meson and muon decays are strongly
modified with respect to transparent sources. Characteristic for neutrino
sources containing photons as scattering targets is a strong energy-dependence
of the ratio $R^0$ of $\nu_\mu$ and $\nu_e$ fluxes at the sources, ranging from
$R^0=\phi_\mu/\phi_e\sim 0$ below threshold to $R^0\sim 4$ close to the energy
where the decay length of charged pions and kaons equals their interaction
length on target photons. Above this energy, the neutrino flux is strongly
suppressed and depends mainly on charm production.
