In this paper I calculate the anisotropic flux of cascade radiation produced by an isotropic distribution of highly relativistic protons immersed in the photon field of a spatially separated point source.
Most radiation is produced towards the source of the target photons.
An astrophysical application of this result is X-ray irradiation of AGN accretion disks by highly dissipative nuclear jets. Low Mach number jets convert a large fraction of their kinetic power into relativistic particles via resonance with MHD turbulence. Consequently, these jets do not show up as radio jets on large scales. Protons can easily reach high energies by stochastic acceleration in the turbulent jet plasma, whereas severe energy losses make it very difficult for the electrons to be accelerated at all. Proton acceleration saturates at the threshold energy for photo-production of secondary particles in the radiation field of the inner accretion disk.