1. Allkofer, O.C.: Introduction to Cosmic Radiation, Verlag Karl Thiemig, München (1975).
2. Belyaev, A.A., et al.: In “Electron-Photon Cascades in Cosmic Rays at Superhigh Energy”, A.T. Abrosimov Ed., Nauka (1980), in Russian.
3. Benecke, J., et al.: Phys. Rev., 188, p. 2159 (1969).
4. Bourdeau, M.F., et al.: J. Phys. G, 1, p. 821 (1975a).
5. Bourdeau, M.F., et al.: PICRC, 8, p. 2878 (1975b).