The atmospheric γ ray spectrum from 50 MeV to 1 GeV at 3 mbar for 4.5- and 12-GV cutoffs and sea level

Abstract

The energy spectrum of the atmospheric γ rays has been measured utilizing the multiple scattering of the electron-positron pairs in a 30-gap spark chamber. The spectrum at 3 mbar and 4.5-GV cutoff is Iγ = (7.9 ± 1.6) × 10−3E−1.45±0.20 γ(s g sr Mev)−1 for 50 < Eγ < 250 MeV and Iγ = (8.7 ± 1.8) × 10−1E−2.3±0.4 γ(s g sr MeV)−1 for 250 < Eγ < 1000 MeV. At 12 GV the intensity is reduced by the factor 0.57. The shape of the spectrum is steeper than that predicted by Beuermann, but the discrepancy can probably be accounted for by uncertainties in the pion production in the atmosphere and in the intensity of the return albedo. The sea level energy spectrum is also fitted by a power law and the angular distribution by a series expansion in cos (nθ).