  The rarest cosmic rays above the GZK cut'off $(E_{CR} \tilde{>} 10^{19} \div
10^{20} eV)$ are probably born at cosmic distances ($\tilde{>}$ tens Mpc) by
AGNs (QSRs, BLac, Blazars...). Their puzzling survival over $2.75 K^o$ BBR
radio waves opacities (the ``GZK cut off'') might find a natural explanation if
the traveling primordial cosmic rays were UHE neutrinos (born by UHE photopion
decay) which are transparent to $\gamma$ or $\nu$ BBR. These UHE$% \nu$ might
scatter onto those (light and cosmological) relic neutrinos clustered around
our galactic halo.
  The branched chain reactions from a primordial nucleon (via photoproduction
of pions and decay to UHE neutrinos) toward the consequent beam dump scattering
on galactic relic neutrinos is at least three order of magnitude more efficient
than any known neutrino interactions with Earth atmosphere or direct nucleon
propagation. Therefore the rarest cosmic rays (as the 320 EeV event) might be
originated at far $(\tilde{>} 100 Mpc)$ distances (as Seyfert galaxy MCG
8-11-11). The needed UHE radiation power is in rough agreement with the NCG
8-11-11 observed in MeV gamma energy total output power. The final chain
products observed on Earth by the Fly's Eye detector might be mainly neutron
and antineutrons as well as, at later stages, protons and antiprotons. These
hadronic products are most probably secondaries of $W^+ W^-$ or $ZZ$ pair
productions and might be consistent with the last AGASA discoveries of 6
doublet and one triplet event.
