Full-Energy peak efficiency of an NaI(Tl) detector with coincidence summing correction showing the effect of the source-to-detector distance

The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ-γ coincidence summing correction factors (CSCF) for a 3″× 3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ-γ CSCF were calculated for 60Co, 133Ba and 152Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (εT), the full-energy peak efficiency (εP) and the effective solid angle (Ωeff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances.