Measurements of the lateral distribution of air shower and its size spectrum in Kobe

The results of measurements of the lateral distribution of charged particles in air shower and its size spectrum are described. Ten plastic scintillators (N-detectors) with 1 m2 of effective area and 5 cm thickness and 54 plastic scintilators (S-detectors) with 0.25 m2 of effective area were used for the detection of the particle density of air shower (EAS). These scintillators were arranged inside and outside of the laboratory. Some scintillators were placed in two-layer arrangement with a 3 mm thick iron plate between the detectors. The energy flow of EAS was measured with 9 lead glass Cherenkov detectors. The system was operated for the period from January to October in 1977, with three trigger conditions which were four-fold-coincidence, two-fold-coincidence and anyone of five designated S-detectors. The following results were obtained from the measurements. The lateral distribution in the range around 50 m was able to be expressed by a single age NKG function. The average value of the age parameter decreased gradually with the increase of size, and approached to a constant value. The ratio of the standard deviation of age to the average value of the age parameter decreased simply with the increase of size. The zenith angle distribution was almost constant. In the size from 8 x 104 to 5 x 106, the observed size spectrum was able to be expressed with a single power function. (Kato, T.)