1. G. M. Wells, Report R.u.D.B.(W)T.N. 146, June 1954, 1958.
2. G. W. C. Tait,Nucleonics, 14 (1956) No. 1, 53.
3. D. C. Stevens, Report AERE, HP/M 110, 1956.
4. D. C. Collins, Report AEC, DP-188, 1956.
5. G. W. C. Tait, J. Beal,Health Phys., 10 (1964) 279.