1. D.L. Williamson, L. Niesen, G. Weyer, R. Sielemann and G. Langouche,Hyperfine Interaction of Defects in Semiconductors, ed. G. Langouche (Elsevier, Amsterdam, 1992) Chap. 1.
2. G. Langouche,Mössbauer Spectroscopy Applied to Inorganic Chemistry, eds. G. Lang and F. Grandjean (Plenum, New York, 1989) Chap. 10.
3. A complete listing of the Mössbauer literature can be found in the monthly issues of the Mössbauer Effects Reference and Data Journal, and in the various subject-oriented compilations edited by the Mössbauer Effect Data Center, University of North Carolina, Asheville, USA.
4. D.V. Lang and R.A. Logan, Phys. Rev. Lett. 39(1977)634.
5. D.V. Lang, R.A. Logan and M. Jaros, Phys. Rev. B19(1979)1015.