1. For detailed discussions, see “Mossbauer Isomer Shift” eds., G.K. Shenoy and F.E. Wagner, North Holland, Amsterdam, (1978).
2. E.R. Bauminger, G.M. Kalvius and I. Nowik, ibid., Chap. 10.
3. E.R. Bauminger, I. Felner, D. Froindlich, D. Levron, I. Nowik, S. Ofer and R. Yanovsky, J. Phys. (Paris), Colloq. 35:C6-61 (1974).
4. B.C. Sales and D. Wohlleben, Phys. Rev. Lett. 35:1240 (1975).
5. W. Franz, F. Steglich, W. Zell, D. Wohlleben and F. Pobell, Phys. Rev. Lett. 45:64 (1980).