The transmitted photon spectra of133Ba, 137Cs, and 60Co sources are measured through different thicknesses of a soil medium. A multiple-scatter peak is observed at an energy of 100 keV independent of incident photon energy and thickness of the medium. The intensity of the peak decreases exponentially with the increase in thickness of the medium. A linear relationship between the effective atomic number of the medium and the multiple-scatter peak energy is observed.