Analyzes of environmental samples regarding their radioactivity is of important concern for health purposes. We need standard sources to determine radioactive components and their activities. These sources are usually produced regarding type of the sample. One of the fundamental and precise tools to recognize radioactive materials and their activities is HPGe Detector. To reach this goal the detector needs to be scaled by standard sources with the same shape and the same components with environmental samples. It is also needed to determine the efficiency of the detector in a wide range of energies. The most precise way to determine detector efficiency is by doing experiment using standard sources. Since experimental methods are time taking and difficult to apply in some cases, it is worth using simulating method which takes a short time and is precise. In the first part of this research the detector efficiency is determined in two different ways: experimental and simulating for energies from 121 keV to 1408 keV for a volume source. In simulating method the Monte Carlo code MCNPX was the results of which were in agreement with experimental data. In the second part, the activity of Eu152 and Cs137 of volume source which is standardized by these components is calculated using efficiencies and simulating outputs and experimental data by Eu152 point source and it is shown that it is possible to use a point source to determine the activity of radionuclide with unrecognized activity in volume environmental samples.
