  During the era of primordial nucleosynthesis the background of
non-equilibrium antineutrinos is being formed due to decays of neutrons and
nuclei of tritium. The spectra of antineutrinos of this background were
calculated taking into account the Coulomb interaction between electron and
daughter nucleus in $\beta^-$-decay. The dependence of these spectra on the
value of the baryon-to-photon ratio $\eta$ at the period of primordial
nucleosynthesis is investigated. The observations of these antineutrinos will
allow us to look directly at the very early Universe and nonequilibrium
processes taken place before, during, and some time after primordial
nucleosynthesis. In any case, this phenomenon is one more aspect in the picture
of the standard cosmological model.
