Energy spectrum of surviving primary protons with energies (3/30) TeV at 5200 m a.s.l. and the cross section for proton--air-nucleus collisions

The energy spectrum of surviving primary cosmic-ray protons without collision in the atmosphere has been obtained from the observation of high-energy nuclear bursts produced by singly charged particles in the energy range 3 TeV to 30 TeV without accompanying air shower particles at Chacaltaya, Bolivia (5200 m a.s.l. or 550 gcm−2 atmospheric depth). Comparison of this spectrum with an extrapolation of the energy spectrum of primary cosmic-ray protons obtained by Ryanet al. to higher energies with the same exponent shows a logarithmic rise of the cross-section for proton-air-nucleus collisions from 3 TeV to 9 TeV.