The study presented in this paper aims to explain the influence of scintillation detector size on spectrometric parameters. For this purpose, a setup composed of 1.5"×1.5", 2"×2" and 3"×3" NaI(Tl) detectors from the same manufacturer was performed. Furthermore, the linearity of detector response to gamma-ray energy was examined for all detectors. Our results show that the energy resolution presents a remarkable dependency to detector size, governed by a second order polynomial function. Thus, the energy resolution shows a significant decrease for almost all energies. As expected, full-energy peak efficiency and Peak-to-Total coefficients have a notable correlation with NaI(Tl) crystal size. In order to study a larger range of crystal sizes, we have developed a Monte Carlo (MC) simulation model using Geant4 (V 10.05). The obtained results were presented using ROOT (V 6.14/08) data analysis framework. The statistical uncertainties were below 4% for all obtained spectra. The comparison of simulated and measured results shows an excellent agreement. The accuracy of our model and the real detector responses has been quantified by applying statistical tests. In this context, a negligible deviation within 4.1% and 3.96% was found, for the obtained response functions and efficiency curves, respectively. An important improvement of intrinsic efficiency and photoelectric effect probability was observed for larger crystals. However, our study shows that CPU-time increases with increasing the active volume of the detector.
Keywords: Energy calibration; Energy resolution; Full-energy peak efficiency; Gamma-ray spectrometry; Geant4; Monte Carlo; NaI(Tl) detector; Peak-to-total; Size effect; Total count.
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