Detector modeling and detector efficiency in GATE simulation

Scintillation detectors are mostly used in nuclear, particle and medical physics, geological exploration and homeland security. In this thesis, it is aimed to determine the calibration factors of the NaI(Tl) scintillation detector system, which is widely used in nuclear physics. The main factors for a successful gamma spectrum analysis are calibrations of energy and energy resolution with the full energy peak efficiency. Detector efficiency for 2"x2" NaI(Tl) was investigated both experimentally and using Geant4 based GATE simulation. Experimental measurements were carried out using NaI(Tl) de- tector with radioactive sources emitting gamma-rays in different energy ranges (59-1408 keV) in Ankara University Faculty of Science Physics Department. The point radioactive sources used in the experiment are 137 Cs, 60 Co, 152 Eu, while the cylindrical ones are 241 Am, 22 Na. The shape and activities of the radioactive sources used in the experimental measurements and detector system were modeled in the GATE simulation. The detector efficiency results obtained from the experiment and simulation were compared. As a result, analytical equations, which are very important in detector efficiency calibrations, have been determined with their parameters. After the experimental and simulation results were be compatible with each other and literature, the simulation model was modified to other scintillation detectors such as LaBr3 (Ce), GAGG(Ce) and SrI2 , and the detector efficiency values for gamma radiation were determined.