Integral energy spectrum of gamma-rays and neutrons at the Sun, emitted in the forward cone (≲10°) for 106 particles. The results are given by the Monte Carlo calculation based on GEANT4. The left-hand panel shows the integral energy spectrum of neutrons (+) and gamma-rays (•) for proton incidence, and the right-hand panel corresponds to the incidence of helium ions. Either protons or helium ions were injected into the solar atmosphere with a power-law index of 3. The maximum energy of ions is set at 100 GeV per nucleon. The fluxes represent the forward-emitted neutrons and gamma-rays to a solar atmosphere thickness of 10 g cm−2. The vertical number represents the expected number of secondary particles (n, γ) with energy higher than En,γ for the injection of 106 protons or helium ions into the solar surface.
