A semiempirical model for atmospheric γ rays from 0.3 to 10 MeV at λ = 40°

We present a model from which the angular and depth dependent atmospheric γ rays can be derived in the energy range of 0.3–10 MeV at λ = 40°. The model consists of an isotropic source function which depends on depth and energy expressed in the form S(E, x) = S0(E)[1 + b(E)x + c(E)x²]e−x/p(E) photons/(g air s MeV) and is determined semiempirically. We determined source strengths for 38 predicted atmospheric γ ray lines and for 10 different energies in the continuum. For the continuum a diffuse cosmic flux, consistent with the Apollo 15/16 data, is assumed in order to fit the measured data above 10 g/cm². Total and directional fluxes are computed at two different atmospheric depths. The computed flux compares well with other measurements and theoretical calculations.