A cloud-chamber investigation of penetrating showers

Abstract

An account is given of a cloud-chamber investigation of penetrating showers. It is concluded that the cloud-chamber data are consistent with Jánossy’s counter data and also with the view that penetrating showers consist of a small number of penetrating ionizing particles which are mainly mesons. There is no evidence to show that the showers are produced by processes other than those postulated in the theory of meson production proposed by Hamilton, Heitler & Peng, together with the addition suggested by Jánossy, i. e. the emission of small groups of mesons every few centimetres of lead. There are given several photographs of showers of penetrating particles which may be examples of the successive production of penetrating particles by an incident nucleon and its recoil particles. The spectrum of the penetrating particles seems to be approximately of the same form as the meson spectrum at sea-level. Some 20% of penetrating showers are accompanied, in the cloud chamber, by what appear to be electron cascades. It is shown that these showers cannot be due to knock-on electrons, to high-energy electron cascades penetrating the whole thickness of the absorber, or to decay electrons unless a meson of lifetime less than 10 -10 sec. is postulated. It is suggested that these showers may be due to electrons or photons produced in processes which become important at very high energies, e. g. > 10 11 eV.