1. Argan P E, Gigli A and Scienti S 1954Nuovo Cimento 11 530
2. Barrett P H, Bollinger L M, Cocconi G, Eisenberg Y and Greisen K 1952Rev. Mod. Phys. 24 133–178
3. Bezrukov I B, Beresnev V I, Nyunin M I, Ryazhaskaya O G and Zatsepin G T 1969Proc. 11th Int. Conf. Cosmic Rays, Budapest 4 285
4. Bezrukov I B, Beresnev V I, Zatsepin G T, Nyunin M I, Ryazhskaya O G and Stepanests L N 1972Soviet J. Nucl. Phys. 15 (2) 176
5. Chin S, Hanayama Y, Hara T, Higashi S, Kitamura T, Miono S, Nakagawa M, Ozaki S, Takahashi T, Tsuji K, Wada T, Watase Y and Shibata H 1969Proc. 11th int. Conf. Cosmic Rays, Budapest 4 59