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2. P. V. Pavlov, E. I. Zonin, D. I. Tetel’Baum andYu. S. Popov:Sov. Phys. Dokl.,10, 786 (1966).
3. W. J. Kleinfender, W. S. Johnson andJ. F. Gibbons:Canad. Journ. Phys.,46, 597 (1968).
4. G. H. Schwuttke, K. Brack, E. E. Gardner andM. M. Deangelis:Radiation Effects in Semiconductors, Ed.F. L. Vook (New York, 1968), p. 406.
5. The wafers were supplied by S.G.S. Fairchild, Agrate (Milano).