The detailed structure of air shower cores

Abstract

An array of 64 large plastic scintillators, 5 Wilson cloud chambers and about 500 G-M counters has been used to study the electronic structure of air-shower cores. It has been found that there is no unique structure function that will describe all cores. Cores can be classed as single, multiple or flat-topped. On average the single cores follow the Nishimura-Kamata distribution with the age parameter slightly greater than unity with the exception of the region within 20 cm of the core. Multiple-cored and flat-topped showers can be simulated by the summation of a number of spatially separated single cores. It is shown that the multiply cored showers cannot be due to cascades produced by the neutral pions from a single interaction but that the core structure is due to the nature of the primary particle. The central density of single-cored showers of a given total size is considerably higher on average than the central density of multiply cored showers of the same size. Up toN=106 the ratio of singly cored showers to others is, within the errors, the same as the ratio of the numbers of protons to other primaries (of the same total energy) at lower energies. AboveN=106 there is a great increase in the ratio of multiply cored to single-cored showers. This suggests that there is a change in the composition of cosmic radiation at about 3·1015 eV. The deficiency of protons above this energy could be due to a failure of the acceleration mechanism and/or to the escape of protons from the galactic disc. Both explanations seem to require that, in the vicinity of the sun, the interstellar magnetic fields should, generally, be considerably less than 10−5 G. Future experiments are discussed.