Experimental and simulated methods to characterize the response of a scintillator detector

The NaI(Tl) detector is one of the most used in gamma ray spectrometry because it presents high counting efficiency for gamma rays in a wide energy range. This study presents the modeling of a real 11/4 x 3/4 " NaI(Tl) scintillation detector + photomultiplier using computational simulations carried out by the MCNP6 code, which considers energy resolution. In the mathematical model, the sensitive volume of the detector was adjusted using Am-241 and Cs-137 radiation sources by means of the absolute photopeak efficiency. Moreover, the MCNP6 code was used to calculate the effective solid angle of the detector in order to obtain the intrinsic efficiency response function. The mathematical model was experimentally validated using calibrated radioactive sources (Am-241, Ba-133, Cs-137 and 60Co) and the response functions efficiency curve and energy resolution were obtained. In addition, an experimental evaluation of the crystal homogeneity of the detector was made using a(137)Cs radiation source and a 3D printed device developed without stepper motors. The proposed methodology is able to obtain absolute photopeak efficiency in agreement with experimental data with maximum relative error of 5.64%. The gamma scanning procedure indicated that the crystal of the detector remained homogeneous.