Momentum spectra, charge ratio, and zenith-angle dependence of cosmic-ray muons

A large rotatable magnetic spectrometer was used to measure the sea-level energy spectra of cosmic-ray muons arriving at 30^∘{} and 75^∘{} zenith angle in the energy range 50-1700 GeV. The measured muon charge ratios and the ratio of the intensities at the two angles imply that the fraction of neutrons in the primary flux at energies above 1 TeV/nucleon is much larger than observed at lower energies and possibly as high as 25%.