1. J. Bonnal, G. Brifford, and C. Manus, Phys. Rev. Letters,6, No. 12, 665 (1961).
2. A. Simon, Phys. Rev.,98, 317 (1955).
3. A. Simon, Proceedings of the Second United Nations International Conference on Peaceful Uses of Atomic Energy, 1958 (United Nations, Geneva, 1958), Vol. 32, p. 343.
4. R. Bickerton, Proc. Phys. Soc. (London),B70, 350 (1957).
5. B. Lehnert, reference 2, p. 349.