Abstract
The momentum spectrum of negative pions in the vertical direction has been measured using the Durham cosmic ray spectrograph in conjunction with an I.G.Y. neutron monitor. Pions were detected by means of their interaction and subsequent neutron production in the monitor.
The ratio of the intensity of charged pions to charged muons is found to vary slowly with energy, being in the range 0.1-0.2% in the region of energy studied.
The pion spectrum has been taken with the energy spectra of protons and muons to give the attenuation length for pions in the atmosphere. This quantity falls from about 160 g cm-2 at 1 GeV to 110 g cm-2 at 100 GeV; the corresponding inelasticity of pion-air-nucleus collisions increases from 50% to 100% over the same energy range.