study of the effect of collimator size on the efficiency of gamma radiation measurements using a scintillation detector

Abstract

This research investigates the effect of collimator size on gamma-ray measurements using a sodium iodide scintillation detector doped with thallium (NaI(Tl)). The gamma-ray sources used in this study were Americium-241 with an energy of 59.5 keV and Cesium-137 with an energy of 662 keV. The collimator sizes tested were 4, 7, 9, and 13 millimeters, including a condition without a collimator. The measured parameters included spectral count rate and energy resolution. The results showed that, for Americium-241, the spectra obtained with 9 mm, 13 mm, and without a collimator yielded the highest count rates, while the 4 mm collimator produced the lowest count rate. In terms of energy resolution, the 4 mm collimator provided the lowest full width at half maximum (FWHM), indicating the best energy discrimination and highest performance. In contrast, measurements without a collimator resulted in the highest FWHM values For Cesium-137, the results followed a similar trend. The highest count rate was observed without a collimator, while the 4 mm collimator yielded the lowest count rate. The energy resolution also showed consistent behavior, with the 4 mm collimator providing the lowest FWHM. Overall, the energy resolution tended to worsen (increase in FWHM) as the collimator aperture size increased, with the no-collimator condition giving the highest FWHM values.