1. P. Hautojärvi (ed.) Positrons in Solids (Springer-Verlag, Heidelberg, 1979).
2. CF, Coleman and A.E. Hughes, in Research Techniques in Non-Destructive Testing ed. RS. Sharpe (Academic Press, London and New York, 1977) Vol. 3, p. 355.
3. A.E. Hughes, Materials in Engineering, 2, 34 (1980).
4. K.G. Lynn, C.M. Wan, R.W. Ure and J.G. Byrne, Phys. Stat. Sol. (a) 22, 731 (1974).
5. K.G. Lynn and J.G. Byrne, Met. Trans. 7A, 604 1976.