Lattice disturbances have been created in otherwise ``perfect'' ice single crystals by high‐energy neutron irradiation. These imperfections act as nucleation centers for internal melting when ir energy is absorbed. The interaction of a single neutron with the ice lattice is marked by one generated Tyndall flower which can easily be localized. A method is described to grow large single crystals of ice having the low concentration of imperfections necessary for the experiment. We also describe a Schlieren optical device with high resolution constructed for the observation of melting figures in the ice crystals.