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We have observed the channeling effects on the transmission of H2 + molecular ions through thin gold crystals. Energy and thickness dependences have been tested in planar channeling conditions. Similarly, the production of H2 + ions from an incident H2 + beam has been studied. All these observations are consistent with a molecular recombination taking place at the back surface of the crystal.

We have observed variations with incident energy of the scattering yield of H+ and He+ ions measured in a particular configuration of planar double alignment. The structure of these variations is related to the oscillating nature of the trajectories of the ions in planar channeling. Experimental oscillation lengths are deduced for H+ and He+ ions in the (111) direction, and for H+ ions in the (110) direction.

In recent years a great deal of theoretical work has been devoted to the description of the interaction of ultrarelativistic electrons and positrons and high energy photons moving along the major directions of crystals.1–9 It was predicted that quantum electrodynamic (QED) effects must be taken into account. In particular, the perfect alignment of photons with a crystal axis was predicted to increase the pair production rate above the Bethe-Heitler (BH) value.