1. U. Gonser: Proc. 2nd Int. Conf. Mössbauer effect, Paris (Wiley Interscience, London, 1962), p. 280
2. G. Lang, W. Marshall: Proc. Phys. Soc. 87, 3 (1966)
3. G. Lang: Phys. Letters 26 A, 223 (1968)
4. E. F. Hartree: Ann. Rept. Prog. Chem. 43, 287 (1946)
5. J. E. Bennett, J. F. Gibson, D. J. E. Ingram: Proc. Roy. Soc. A 240, (1957)