1. Sköld, K., Rowe, J.M., Ostrowski, G., Randolph, P.D.: Phys. Rev. A6, 1107 (1972)
2. Sakamoto, M., Brockhouse, B.N., Johnson, R.H., Pope, N.K.: J. phys. Soc. Japan17, Suppl. B-II, 370 (1962)
3. Egelstaff, P.A., Haywood, B.C., Thorson, I.M.: Inelastic Scattering of Neutrons in Solids and Liquids, Vol. I, p. 343. Vienna: IAEA 1963
4. Dorner, B., Plesser, Th., Stiller, H.: Discuss. Farady Soc.43, 160 (1967)
5. Copley, J.R.D., Rowe, J.M.: Phys. Rev. Letter32, 49 (1974)