抄録
Nuclear events produced by secondary shower particles of cosmic rays have been observed in a cloud chamber operated at Mt. Norikura, 2,840 meters altitude. In the chamber were mounted lead and carbon plates, and a comparison was made for penetrating showers originating in these two materials. The results show that the nuclear cross sections for lead and carbon are given to be in the ratio of geometrical values. The multiplicities of shower particles in lead are difenitely larger than those in carbon, and the angular distributions, however, show no differences in both cases. These results can be interpreted quite naturally if we consider that the shower particles contain inevitably high energy protons besides mesons and that the created meson or recoiled proton which is emitted at large angle from the initial direction of the colliding particle has no sufficient energy to produce energetic particles.
