The strongly interacting particles in air shower cores

Abstract

The results of an experiment to study the strongly interacting particles in air shower cores are presented. The experiment used 64 large plastic scintillators in three different close configurations, two Wilson cloud chambers, about 600 G-M counters and 100 tons of lead. It is shown that there is no unique structure function for the strongly interacting particles which will fit all showers. Rather, showers can be classed as single-core or multi-core. The multi-core showers can have various numbers of cores from 2 upwards. Single-cored showers appear to be due to proton primaries; multi-cored showers to be due to primaries of A.≥2. There is some evidence that deuterons form about 5% of the hydrogen nuclei in the cosmic radiation at total energies of ∼ 4. 1014 eV. It seems likely that the only shower of size > 107 particles whose core hit the shielded scintillators was due to a very heavy nucleus, possibly iron. Above a shower size of 106 particles we have observed 47 multi-cored showers and 7 single-cored showers. Between sizes of 105 and 106 particles we have seen 68 multi-cored showers and 85 single-cored showers. It has proved possible with this apparatus not only to study individual showers in detail, but also individual nuclear interactions in these showers. The methods of doing this are explained and discussed. In contrast with much emulsion work the surviving baryon can often be easily identified and its momentum determined. It is found that the elasticity in individual nucleon-air nucleus collisions varies from 0.3 to 0.7 with a median value of 0.54. A method of obtaining the average value of the elasticity for energies of 1012 to 1016 eV is described. In ∼ 400 individual mesons studied none were found with transverse momenta in the region ≥ 4 GeV/c and all had values consistent with a mean of 0.4 GeV/c. Interactions were identified at heights above the array varying from 25 metres to 4 kilometres. This is consistent with an interaction mean free path of protons in air of ∼ 90 g/cm2. This value is confirmed by an independent measurement of the total number of collisions suffered by 14 proton primaries. The results are compared with previous experiments and their implications discussed.