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2. Basson, J.K. (1970) : In : Proceedings, Pneumoconiosis conference p 561. Editor : H.A. Shapiro. Oxford University Press, Cape Town - London - New York - Toronto.
3. Greig, J.D. and Freed, C.C.: Ibid p 565.
4. Conference on Occupational Health Experience with Uranium (1975) : ERDA 93. Editor McDonald E. Wren. U.S. Government Printing Office, Washington DC.
5. International Commission on Radiological Protection (1964) : ICRP Publication 6. Pergamon Press, Oxford - London - New York - Paris.