An estimate of the secondary-proton spectrum at small atmospheric depths

We have calculated the energy spectrum of secondary protons produced in the atmosphere as a function of the atmospheric depth and zenith angles at a location with zero geomagnetic cut-off. In this calculation, we have included all relevant energy losses and production processes. It is shown that the protons produced from the target nuclei through recoil and evaporation processes dominate the spectrum below 350 MeV; These calculations have been carried out over an energy region from 20 MeV to 40 GeV and up to a depth of 40 g/cm(2) of the atmosphere over a latitude with zero geomagnetic cut-off for both the periods of minimum and maximum solar modulation.