1. Heisenberg, W.: Cosmic radiation. New York: Dover Publications 1946; Z. Phys. 133 (1952) 65.
2. Fermi, E.: Phys. Rev. 81 (1951) 683; 92 (1953) 452; 93 (1954) 1434.
3. Landau, L., Lifshitz, E.: The classical theory of fields (translated by M. Hamermesh). Cambridge, USA: Addison-Wesley Press. 1951, p. 31.
4. Marshak, R. E.: Meson physics. New York: McGraw Hill Book Company 1952.
5. Gell-Mann, M., Watson, K. M.: Ann. Rev. Nucl. Sci. 4 (1954) 219.