Bradt H L and Peters B 1950Phys. Rev. 77 54
Cheshire D Let al 1974Phys. Rev. D10 25
Lindstrom P J, Greiner D E and Heckman H H 1972Bull. Am. Phys. Soc. 17 488
Verma S D and Herzo D 1973Proc. 13th Int. Conf. Cosmic Rays, Denver Vol. 4, p. 2883
Verma S D and Norckauer H R 1975Proc. 14th Int. Conf. Cosmic Rays, Munich Vol. 9, p. 3183