Muon interactions in the energy range 5 to 1 000 GeV
The Durham Horizontal Spectrograph has been used to study the variation with energy of the frequency of electromagnetic interactions of muons. A considerable increase in the frequency of occurrence of electromagnetic showers with muon energy is observed and is attributable in the main to direct pair production. The form of the variation with energy of the interaction probabilities and the frequency of successive interactions of the same particle are consistent with all the particles being muons, and it is concluded that there is no evidence in favor of the existence of particles having an unusually high probability of burst production–the X particles postulated by Vernov et al. (1966)–at least in the near-horizontal cosmic-ray beam at ground level.