1. R. Leachman and C. Kazek, Phys. Rev.,105, 1511 (1957).
2. R. Leachman, Phys. Rev.,101, 1005 (1956).
3. J. Terrel, Phys. Rev.,113, 527 (1959).
4. H. Bowman and S. Thompson, Proc. of the Second Intern. Conf. on the Peaceful Uses of Atomic Energy, Geneva, UNO, Vol. 15 (1958), p. 212.
5. A. Smith, et. al.,Idem,, p. 392.