1. S. M. Ryvkin, Sov. Phys. Solid State 7(4), 1035 (1965).
2. S. M. Ryvkin, A. A. Grinberg, and N. I. Kramer, Sov. Phys. Solid State 7(7), 1766 (1965).
3. N. I. Kramer, Sov. Phys. Solid State 7(12), 2874 (1965).
4. A. A. Grinberg, Proc. the 6th Winter School on the Theory of Nucleus and High-Energy Physics (FTI AN SSSR, Leningrad, 1971), Part 3, p. 29.
5. A. A. Rogachev and S. M. Ryvkin, Sov. Phys. Solid State 7(7), 1774 (1965).