So far, there has been a lot of research in different countries, including Iran, on gamma radiation caused by radioactive elements such as soil, rock, etc. We are exposed to this radiation, if we receive more than standard values we will face poisoning and other side effects. As we spend most of our time indoors today, studying the radioactivity of building materials is important. In this study, we investigate the radioactivity of,, and in 10 decorative granite stones of Iran samples by n-type HPGe detector GMX40P4-76, manufactured by ORTEC company. The amount of activity obtained was 4.3493-1143.3456, 0.40959 -61.3426, 0.8651-135.2603 and 109.0161-1916.25098 for,, and. These activities are higher than the reported global average. Absorbent dose rate ranges from 7.5726 to 1842.842, as well as internal and external annual effective dose rates and internal and external risk indices for the samples. According to the results, almost 90% of these samples have exceeded permitted values, so it is advisable to use them on the exterior of the building and it is advisable to observe the requirements for interior use. Due to the timeliness of experimental measurements and the need for standard springs of the same type and material for detection and calibration of radioactive springs, simulation method will be used to estimate the detector efficiency, which in terms of time And the cost is more affordable. To do this, we will simulate the detector using the exact dimensions and geometry of the detector using the Monte Carlo MCNPX version 2.6 code, then change the thickness of the detector's dead layer closest to the experimental efficiency. We obtain the standard soil source and finally the obtained results will be compared with the experimental results.
