1. Achter,F.K., Meyer,L. (1969): Phys. Rev. 188, 291
2. Akhiezer,A.I., Akhiezer,I.Ya., PomeranchuV T.Ya. (1962): Soviet Phys. JETP 14, 343
3. Aldrich,C.H. (1974): Thesis, University of Illinois, Urbana
4. Allen,G., Higgins,J.S. (1973): Rept. Progr. Phys. 36, 1073
5. Bacon,G.E. (1975): Neutron Diffraction ( Oxford University Press, Oxford )