A Study of Core Structure in Extensive Air Showers by Means of Large Cloud Chamber

Abstract

The core of EAS was observed by large multiplate cloud chamber and scintillation detectors at Mt. Norikura. 8,100 cloud chamber pictures were obtained by various triggering method. Fluctuation of core structure was shown by many typical cloud chamber pictures and were discussed on them at point of view of these pictures. No high energy particle with energy >10¹² eV was found over 2 m from the axis of EAS. For small air shower, characters of the core vary largely even for the same size and age. Proportion of cores which consist of only electromagnetic cascade shower are about a half. On the other hand, particle density and energy density show small fluctuation for large size air shower of s>0.8. As special example, double core and mu-meson bundle events are found and analyzed. A lateral distribution of mean energy of electromagnetic component is expressed by \barE=1.3×10⁹r^{−(0.6±0.15)} eV in region 0.5 to 15 m from the shower axis.