1. Tishin V. G.: Thesis JINR. Dubna 1967.
2. Zhukov G. P., Zabiyakin G. I., Shibayev V. D.: Proceedings of the 6th Conference on Radioelectronics, Vol. 3, Part 2. Atomizdat, Moskva 1965, 191.
3. Groshev L. V., Demidov A. M., Lushczenko V. N.: Izv. AN SSSR, phys. ser.24 (1960), 833.
4. Vrzal J. et al.: Izv. AN SSSR, phys. ser.31 (1967), 1647.
5. Freedman M. S., Porter F. T., Wagner F.: Phys. Rev.151 (1966), 899.