kinematical theory of diffraction contrast has been applied to distinguish between vacancy and interstitial clusters. Interstitial clusters are the only ones which have been positively identified. The annealing of the clusters of defects has been studied in detail and activation energies derived. The disappearance of the X-ray lattice parameter change correlates well with the clustering of interstitial atoms.
97. Electron microscope observations on radiation damage on graphite*
W. Bollman and G. Hennig (Argonne National Laboratory, Argonne, IZZ&ois). Graphite single crystals which have been subjected to different kinds of irradiation have been examined in the electron microscope. Neutron bombardments were carried out within hollow fuel elements to enhance the high energy knock-ons. The flux ranged between nvt= 1O1' and 10"". Electron irradiation at 1 MeV were carried out to produce damage consisting mainly of isolated Frenkel pairs. Irradiations with fission fragments were studied to search for tracks of concentrated damage. Bombardments with C?" ions, accelerated to an energy of 50 keV, produced a local excess of interstitials and permitted a study of their annealing unaffected by vacancies. *Based on work performed under the auspices of the U.S. Atomic Energy Commission.