1. G. J. Budker, CERN Symposium 1956, p. 68.
2. D. C. dePackh,Third International Conference on Ionization Phenomena in Gases(Italian Physical Society, Venice, Italy, 1957), p. 236.
3. D. C. dePackh,Second International Conference on the Peaceful Uses of Atomic Energy, (United Nations, Geneva, Switzerland, 1958), Vol. 30, p. 158.