The Monte Carlo neutron and photon transport code SAM-CE has been used to calculate the photon radiation field in the air-over-ground geometry. It is shown that the external gamma exposure from Gaussian clouds is, for low energies, considerably reduced by the presence of the ground. Organ dose from point sources in the air and from plane sources on the ground have been calculated for several hundreds of radionuclides. In the second case, compared to results of other authors, higher doses were found for medium and high gamma energies, since the relatively low self-shielding of the human body against horizontal irradiations has been accounted for in this paper. For low gamma energies the doses are considerably reduced due to the, in this energy range, stronger shielding of surface roughness of the air-ground interface.