Neutrino Detection by Resonance Absorption in Crystals at Low Temperatures

An experiment is proposed wherein neutrinos emitted during electron capture by radioactive impurities in one part of a crystal may be resonantly absorbed by atoms in another part. Essential to the argument is the fact, recently experimentally proved by M\"ossbauer for gamma rays, that in an emission or absorption by a nucleus bound in a crystal at low temperature the recoil energy is often taken up by the crystal as a whole, with no phonons emitted or absorbed. Thus no energy is lost to recoil, and a neutrino emitted in a monoenergetic process has exactly the right energy to be resonantly absorbed in the inverse process. The feasibility of the experiment depends on the degree to which the electronic impurity levels are broadened relative to the natural width of the neutrino line.