1. N. Kreidl and J. Hensler, J. Amer. Ceram. Soc.38, No. 12, 423 (1955).
2. J. Schulman et al., Nucleonics11, 52 (1953).
3. S. Davison et al., Nucleonics14, 1 (1956).
4. J. Malsky et al., Trans. N. Y. Acad. Sci., November 17, 104 (1955).
5. S. M. Brekhovskikh, Steklo i Keramika1, 3 (1958).