Study of extensive air showers at Mount Norikura. I. Measurement of lateral structure

Abstract

The lateral density distribution of charged particles in EAS is one of the essential parameters for the analysis of individual EAS. To measure the lateral density distribution in detail, 100 ¼-m² scintillators were arranged in a lattice configuration with a unit distance of 5 m or 2.5 m. The conventional EAS array of 20 scintillators was also used to obtain densities up to about 100 m from the center. These observations are much more accurate than those obtained previously, and it has been found that there are various types of structure functions which can be approximated by the functions for single cascades of age parameter from 0.6 to 1.6. It was difficult in some instances to fit the lateral distribution by a unique function, especially for small EAS.The two-dimensional map obtained by means of the above 100 detectors shows that individual EAS have rarely a complicated structure within a range of about 20 m from the axis. The results are discussed in relation to the character of high-energy interactions as well as to fluctuations in the development of EAS.