The possible formation of the neutron drop nA-ZpZ composed of Nn = A - Z neutrons and Np = Z protons in metal hydrides and deuterides is discussed on the basis of experimental facts using the evaporation model of the decay of the compound nucleus. Exotic nuclei and the neutron drop will be formed at a region with a high neutron density in crystals including hydrogen isotopes. Successful explanation of the anomalous nuclear reaction phenomenon in solids by models assuming neutrons in a solid lattice is legitimated.