  We propose to use the threshold-free process of neutrino capture on
beta-decaying nuclei (NCB) using all available candidate nuclei in the Milky
Way as target material in order to detect the presence of the Cosmic neutrino
background. By integrating over the lifetime of the galaxy one might be able to
see the effect of NCB processes as a slightly eschewed abundance ratio of
selected beta-decaying nuclei. First, the candidates must be chosen so that
both the mother and daughter nuclei have a lifetime comparable to that of the
Milky Way or the signal could be easily washed out by additional decays.
Secondly, relic neutrinos have so low energy that their de Broglie wavelengths
are macroscopic and they may therefore scatter coherently on the electronic
cloud of the candidate atoms. One must therefore compare the cross sections for
the two processes (induced beta-decay by neutrino capture, and coherent
scattering of the neutrinos on atomic nuclei) before drawing any conclusions.
Finally, the density of target nuclei in the galaxy must be calculated. We
assume supernovae as the only production source and approximate the neutrino
density as a homogenous background. Here we perform the full calculation for
187-Re and 138-La and find that one needs abundance measurements with 24 digit
precision in order to detect the effect of relic neutrinos. Or alternatively an
enhancement of of the relic neutrino density by a factor of $10^{15}$ to
produce an effect within the current abundance measurement precision.
