NUCLEAR reactions initiated by heavy nucleons involve the transfer of considerable energy from the incident particle to the target nucleus. The amount of energy carried off by the recoiling nucleus is generally sufficient to break chemical bonds, or in irradiated crystalline substances to move the atom to a new site in the lattice. Little information is available about the chemical form in which these recoil atoms come to rest, but useful surveys of previous work have been given by Libby1, and by Edwards and Davies2. A study of the literature shows that the knowledge of chemical behaviour following high-energy particle bombardments is especially lacking, the well-known Szilard–Chalmers effect having been mainly studied with slow neutrons.