Secondary Electrons and Photons in the Upper Atmosphere

Abstract

We present a theoretical and experimental study of the production and propagation of atmospheric secondary negatrons,positrons, and photons moving in the vertical direction. The one-dimensional transport equations have been solved numerically to obtain energy spectra and intensity versus depth for energies as low as 4 Mev and for atmospheric depths up to 400 g/cm^2. The calculations are performed for the solar modulation level of 1968 and geomagnetic cutoff values of zero and 4.5 Gv. We also present experimental data on negatrons and positrons in the energy range from 6.5 to 200 Mev obtained from balloon observations near Ft.Churchill, Canada,in 1968.The comparisons with measurements confirm the calculated energy spectra and intensity versus depth. The spectral shapes of secondary negatrons and positrons are found to be very dependent upon the atmospheric depth.In the high atmosphere, the photonspectrum below •70 Mevis dominated by bremsstrahlung from primary and reentrant albedo electrons rather than by,r^ø decays. The derived intensity versus depth deviates distinctly from the commonly assumed linear growth of the secondary flux with increasing depth.Our results on the functional depth dependence are useful for determining the contribution from atmospheric secondaries to measurements of the electron(and photon)flux at balloon altitudes.