Orientation dependence of intensity and energy loss of hyperchanneled ions

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Abstract
Energy loss measurements are reported for 21.6–60 MeV 127I and 3 MeV 4He ions transmitted through thin single crystals of Au and Ag along directions parallel or nearly parallel to 〈110〉 directions in the crystals. A systematic investigation of 21.6 MeV 127I ions in Ag indicates that for incidence angles within 0.12° of [O11] up to 10 percent of the transmitted ions have energy losses significantly lower than that for ions transmitted parallel to (111). The behavior of these ions is consistent with that expected for ions which are confined within one particular axial channel throughout the crystal. This specific type of axial channeling we call hyperchanneling. The data for hyperchanneled 21.6 MeV 127I in Ag are analyzed in detail and discussed in terms of a theory developed on the basis of potential energy contours obtained from the continuum potentials of the surrounding rows of atoms. Comparison of theory and experiment suggests that these ions undergo more multiple scattering than can be accounted for and that potentials for interactions of ions and free atoms are not entirely adequate for interactions of ions and atoms in a solid.