Statistical equilibrium in particle channeling.

We have used a unique sample configuration consisting of thin, epitaxial films of Ge sandwiched within a Si(100) lattice to explore the conditions for statistical equilibrium in particle channeling. Indications of nonequilibrium came about from a strong asymmetry in the off-normal angular scans. We find the depth necessary to achieve statistical equilibrium to be ~2200angstroms for a 1.8 MeV He particle channeling along the Si direction. This measurement provides a useful guide for the interpretation of channeling experiments in a variety of near-surface applications.