1. W. Bolse, P. Wodniecki, H. Schröder, M. Uhrmacher and K.P. Lieb, Phys. Lett. 93A(1983)429.
2. H. Schröder, diploma thesis, Göttingen (1981), unpubl.; W. Bolse, diploma thesis, Göttingen (1982), unpubl.
3. H. Frauenfelder and R.M. Steffen, in: Alpha, beta and gamma ray spectroscopy, vol. II, ed. K. Siegbahn (North-Holland, Amsterdam, 1960).
4. A.F. Pasquevich, et al., Phys. Lett. 82A(1981) 34; Phys. Rev. B27(1983)863.
5. R.O. Simmons and R.W. Baluufi, Phys. Rev. 103(1956)600; F. Ramsteiner, W. Schüle and A. Seeger, phys. stat. sol. 2(1962)1005.