Calibration of a 5x5 NaI(Tl) for Prompt In-Situ Gamma-ray Spectrometry System

It is important to determine the presence of different radionuclides in the environment at all times in order to control and assess the risk level they pose to the environment. Laboratory and in-situ gamma-ray spectrometry can be used for detecting, monitoring, and assessing levels of radioactivity and radiation dose rates in the environment due to both natural and artificial sources. In this study, the greatest challenge in the calibration of detectors for in-situ gamma spectrometry has been solved. Calibration factors that can be used to convert the net count rates of collected spectrum's photopeak using a portable gamma-ray spectrometer, to quantitative specific activities have been derived. Calibration pads were simulated using standard materials RGU, RGK, and RGTh from International Atomic Energy Agency (IAEA). Region of interest (ROI) were carefully determined around these photopeaks in order to obtain count rates due to each radionuclide under its reference peak. The conversion factors obtained are reliable.