Secondary electron spectrum in the upper atmosphere

The secondary electron spectrum in the upper atmosphere(< 10 g/cm ²) is investigated on the basis of the atmospheric gamma ray spectrum above 30 GeV obtained from our emulsion chamber experiments at balloon altitudes. We have to subtract these electrons produced by nuclear interactions from observed electrons to get the primary electron spectrum in the Galaxy. Thus it is required to precise estimates of secondary electron abundance. Both electron and gamma ray intensities are simultaneously solved using the one-dimensional cascade shower theory plus gamma ray production rate derived from observed data. Secondary electrons increases qualitatively as the depth squared. The secondary spectrum has the same index as atmospheric gamma ray index -2.73, namely proton index, while the primary electron index is rather steeper than that. Therefore the ratio of secondary to primary electrons rapidly increases in the TeV region, and the high altitude is essential for TeV electron experiments.