An Experimental Study of Extensive Air Showers

抄録

An observation of extensive air showers has been performed at Mt. Norikura (2840 m above sea level and 25°N geomagnetic latitude) by the aid of two multiplate cloud chambers, sparsely distributed 90 GM counters and two sets of counter hodoscope pile. In this experiment, the structure of the air shower in the neighbourhood of shower axis was mainly investigated.
For each observed air shower, the shower size, N, and the location of the shower axis were estimated. The air showers were divided into three groups characterized by the core structure which depends upon the shower size. The first group is of the small size shower (less than 1.5×10⁵) which has comparatively poor core which fluctuates by the behaviour of a few high energy particles. The second group is of the middle size shower (1.5×10⁵–5.5×10⁵) in which the decaying nuclear component and the electron component are in state of equilibrium, and the electron component lateraly distributes as proportional to 1/r in particle density and 1/r² in energy flow near shower cores. The third group is of the large size shower (larger than 5.5×10⁵) which contains many high energy nucleons and they are thought to be yet in the state of active nuclear cascade.
Integral size spectrum was obtained as 6.1×10⁻⁹(N⁄10⁵)^−1.5 cm⁻² sec⁻¹ sr⁻¹ for the showers with a total number of particles 1.5×10⁵–5.5×10⁵ and for large size showers the exponent of the spectrum increases with shower size reaching about −1.9 at N=10⁶.