  The cosmic background neutrino of temperature 1.9 K affects rates of
radiative emission of neutrino pair (RENP) from metastable excited atoms, since
its presence blocks the pair emission by the Pauli exclusion principle. We
quantitatively investigate how the Pauli blocking distorts the photon energy
spectrum and calculate its sensitivity to cosmic parameters such as the
neutrino temperature and its chemical potential. Important quantities for high
sensitivities to these parameter measurement are found to be the level spacing
of atomic de-excitation and the unknown mass value of lightest neutrino, in
particular their mutual relation.
