  A possiblity of measuring the cosmic neutrino temperature $\sim 1.9 K$ and
other important quantities such as the chemical potential $\mu$ and the
decoupling temperature $T_d$ is discussed, using the recently proposed process
of photon irradiated neutrino pair emission from metastable atoms. The Pauli
blocking effect of relic neutrinos reduces the rate by a large factor $\approx
(1 + m_1/T_d)/4$ at the threshold of the lightest neutrino pair (of mass
$2m_1$). Correction of linear order in $\mu$ near the mass thresholds can be
used to improve the constraint on the lepton asymmetry.
