1. J. A. Davies, Channeling: Theory, Observation and Applications, ed. by D.V. Morgan (John Wiley, 1973 ), p. 391.
2. S.T. Picraux, New Uses of Ion Accelerators, ed. by J.F. Ziegler ( Plenum Press, N.Y., 1975 ), p. 229.
3. M.A. Kumakhov, Phys. Lett. A32, 558 (1970); Radiat. Eff. 15, 85 (1972).
4. J.U. Andersen, O. Andreasen, J.A. Davies, and E. Uggerhoj, Radiat. Eff. 7, 25 (197l).
5. R.B. Alexander, P.T. Callaghan, and J.M. Poate, Phys. Rev. B9, 3022 (1974).