1. R. Crick, N. Berard, and D. Wilder, J. Nucl. Mater.,27, No. 1, 97 (1968).
2. C. Leitten and R. Beaver, Nucl. Appl.,4, No. 6, 398 (1968).
3. V. E. Réi, Production of Moderator Rods for Nuclear Reactors [in Russian], Atomizdat, Moscow (1965), p. 246.
4. N. A. Toropov et al., State Diagrams for Silicate Systems [in Russian], No. 1, Nauka, Leningrad (1969).
5. E. V. Kolontsova and É. E. Kulago, Kristallografiya,17, No. 6, 1197 (1972).