1. Dementiev E. N. et al. Sov. Phys. Tech. Phys., 25 (1980) 1001; Kienle P. and Schiffer J. P., Z. Phys. A, 321 (1985) 181.
2. Rahman A. and Schiffer J. P., Phys. Rev. Lett., 57 (1986) 1133.
3. Schiffer J. P., in Proceedings of the Workshop on Crystalline Ion Beams, edited by R. W. Hasse, I. Hofmann and D. Liesen (Wertheim) 1988, p. 2.
4. Hasse R. W. and Schiffer J. P., in Proceedings of the Workshop on Crystalline Ion Beams, edited by R. W. Hasse, I. Hofmann and D. Liesen (Wertheim) 1988; Ann. Phys., 203 (1990) 419.
5. Birkl G., Kassner S. and Walther H., Nature (London), 357 (1992) 310; Waki I., Kassner S. et al., Phys. Rev. Lett., 68 (1992) 2007.