In this research, a 12 1”x1” NaI(Tl) detectors gamma-ray detection system was calibrated and tested for measurement of gamma-rays under various conditions. The detectors were connected to a 12-channel counter consisted of counters/rate meters, single channel analyzers and high voltage power supply units. The system was connected to a microcomputer via a serial port for controlling, parameter setting, and displaying/transferring of counting data. Moreover, the Thailand Institute of Nuclear Technology (Public Organization) or TINT has developed a software allowing the user to perform parameter settings and to observe real-time counting data of all detectors graphically on the screen. Firstly, the 12 detectors were caGamma rayslibrated by placing a 100 µCi (3.7 MBq) Cs-137 source at the center of a circle of 24 cm radius while the detectors were placed facing the source along the perimeter of the circle. The relative counting data obtained would be used to normalize the counting rate of each detector for the next measurements. Later, the detectors were arranged along the perimeters of a 60x60 cm square and a 60x90 cm rectangle while the source was placed at different positions within the rectangle and the square respectively. It was found that the obtained counting rates depended upon the distances between the source and the detectors in all cases. The results indicated that this system could be used to assess position of the gamma-ray source. Effects of detector collimation on the counting rate and on the accuracy of the source position assessment were also investigated. Finally, the detectors were arranged along the wall of a 2.6 m x 3 m room with 2 gamma-ray sources at different position.
