Investigation of the pile-up and summation effects on the calibration curves of boron concentration measurement in PGNAA

In the previous research, the self-shielding effect in boron concentration measurement using PGNAA method was corrected by an internal standard material. After correction of the self-shielding, the calibration curve still has some curvature that was not seen in the calibration curve related to simulations spectra. The basic difference between the simulations and experiments was that the actual detection process in an HPGe detector and its related electronics were not simulated. The reason of this difference is the pile-up and summation effects on the spectra during the experiments. In this study, the pile-up and summation effects have been investigated at the different peaks of the spectra. Two methods have been proposed to correct these effects. In the first method, a suitable peak from the spectrum of the internal standard material has been selected and the self-shielding effect has been corrected and in the second method, the mass of the standard samples and the spectrometry time have been reduced and increased, respectively. The results of these methods have been evaluated by different experiments. Results shows that in the correction of the self-shielding effect, the 788 keV + 786 keV peak of chlorine has the best performance. Among the calibration curves plotted with different chlorine peaks, the curve plotted using 788 keV + 786 keV peak had the best linearity. The R-square of this curve was 0.99891. Also, it was found that reducing the mass of the standard samples used to obtain the calibration curve, reduces the nonlinearity caused by the pile-up and summation effects on the calibration curve. By reducing the volume of standard samples used to obtain the calibration curve from 10 ml to 4 ml, the R-squared of the calibration curve obtained in the first method increased from 0.99891 to 0.99904.