Probing low energy neutrino backgrounds with neutrino capture on beta decaying nuclei

We study the interaction of low energy neutrinos on nuclei that spontaneously undergo beta decay showing that the product of the cross section and the neutrino velocity takes values as high as 10−42 cm2 c for some specific nuclei that decay via allowed transitions. The absence of an energy threshold and the value of the cross section single out these processes as providing a promising though very demanding approach for future experiments aimed at a direct detection of low energy neutrino backgrounds such as the cosmological relic neutrinos.