1. O. Czyżewski, B. Escoubès, Y. Goldschmidt-Clermont, M. Guinea-Moorhead, D. R. O. Morrison andS. De Unamuno-Escoubès:Phys. Lett.,15, 188 (1965).
2. D. R. O. Morrison: Report onBristol Conference, January 1963, see also CERN/TC/Physics 63-1.
3. C. B. A. McCusker, L. S. Peak andR. L. S. Woolcott:Proc. Int. Conf. Cosmic Rays (London, 1965), p. 857.
4. W. S. Barashenkov:Cross-sections for interactions of elementary particles (Moscow, 1966).
5. F. F. Abraham, J. Kidd, M. Koshiba, R. Levi Setti, C. H. Tsao andW. Wolter:Nuovo Cimento,28, 21 (1963).