Astroparticle Physics

7.1 Propagation in the Atmosphere 145height in the atmosphere [km]35302520151050photon showerE 0 = 100 TeVθ = 0 °–6–4–2distance from the shower axis [km]035hadronsmuonsγ, e + , e − 302520151050246height in the atmosphere [km]proton showerE 0 = 100 TeVθ = 0 °–6–4–2distance from the shower axis [km]0hadronsmuonsFig. 7.8Comparison of the development ofelectromagnetic (100 TeV photon)and hadronic cascades (100 TeVproton) in the atmosphere. Only2 4 6 secondaries with E ≥ 1 GeV areshown {22}Fig. 7.9Particle composition in theatmosphere as a function ofatmospheric depthBecause of the steepness of the energy spectra the particleintensities are of course dominated by low-energy particles.These low-energy particles, however, are mostly ofsecondary origin. If only particles with energies in excess of1 GeV are counted, a different picture emerges (Fig. 7.10). sea-level compositionPrimary nucleons (protons and neutrons) with the initialhigh energies dominate over all other particle speciesdown to altitudes of 9 km, where muons take over. Becauseof the low interaction probability of neutrinos these particlesare practically not at all absorbed in the atmosphere.