1. J. Badier, M. Demoulin, J. Goldberg, B. P. Gregory, C. Pelletier, A. Rouge, M. Ville, B. Barloutattd, A. Leveque, C. Lovedec, J. Meter, P. Schlein, A. Verglas, D. J. Holthuizen, W. Hoogland, J. C. Klutver andA. G. Tenner:Phys. Lett.,19, 612 (1965);A. Bougé: D. So. Thesis (Paris, 1969), unpublished.
2. D. Merril el al.: Nucl. Phys.,318, 403 (1970).
3. V. Chaloupka, C. Bricman, A. Barbaro-Galtieri, D. M. Chew, R. L. Kelly, T. A. Lasinski, A. Rittenberg, A. H. Rosenfeld, T. G. Trippe, F. Uchiyama, N. Barash-Schmidt, P. Soding andM. Roos (Particle Data Group):Phys. Lett,50 B, 1 (1974).
4. Particle Data Group:Phys. Lett. B,50, 1 (1974) quotes a rate of (8.6±1.8)%; up-to-date sources are listed in ((6), ref. (3)).
5. Particle Data Group:Phys. Lett. B,50, 1 (1974) quotes a rate ot 41 %; up-to-date sources are listed in ((6), ref. (4)).