Monte-Carlo modeling allows calculating the detector efficiency in gamma spectrometry of environmental samples with taking into consideration both the photon selfabsorption in sample itself and absorption in all other materials between the sample and the detector’s active part. In this paper, the peak efficiencies of the Hp Ge detector (GMX) for gammas at various energies (emitted isotropically from the standard disk source and volumetric source - environmental sample, in which the different radionuclides are present) .