بررسی مکان و راستای آشکارساز جهت مینیمم نمودن ضریب انباشت شار پرتوهای گاما

The purpose of this study is to select the best place for the detector towards shield and the gamma source which have the least flux buildup factor of the photon. In this research, the flux buildup factor of gamma rays was calculated by using of MCNP-4C code for cylindrical sources 137Cs, 60Co, 16N coaxial shields made up of aluminum, iron and lead with a constant thickness 1.55 cm in detector CsI (Tl). For this purpose, detector was respectively placed at different distances from 9 to 18 cm and different angles from 30 to 150 degrees with respect to the axis of the source. In this study, we tried to assess the dependency of the buildup factor with material atomic number, gamma-ray energy, relative distance of detector-material-source and angle of detector to source. The obtained results showed that the buildup factor values are variable in a wide range from 1 to 3.5. According to the results of simulation, if the aim is reduction of the buildup factor source, shield and detector should be designed parallel and coaxial. Otherwise, whatever deviation of detector from the central axis is increased, the gamma-rays buildup factors are greater in detector.