No abstract

The high quality measurements of neutron energy spectra are required in various fields of research and applications. However, in many cases the contribution of gamma background causes the inaccuracy of neutron spectrum. Therefore, the discrimination of gamma-ray events in neutron spectrum is necessary. In this article, an algorithm for digital implementation of the chargecomparison method for n/γ discrimination based on Digital Signal Processing technique is described. Furthermore, the APX-500 board was used as a hardware for the development of a Pulse Shape Disciminator, and is equipped with ADC ADM-414 14 bit-100 MSPS. The fully system has been tested with EJ-301 detector, using 252Cf neutron source.

The ability to distinguish between neutrons and gamma-rays is important in the fast -neutron detection, especially when using the scintillation detector. A dual correlation pattern recognition (DCPR) method that was based on the correlation pattern recognition technique has been developed for classification of neutron/gamma events from a scintillation detector. In this study, an EJ-301 liquid scintillation (EJ301) detector was used to detect neutrons and gamma-rays from the 60Co and 252Cf sources; the EJ301 detector's pulses were digitized by a digital oscilloscope and its pulse-shape discriminant (PSD) parameters were calculated by the correlation pattern recognition(CPR) method with the reference neutron and gamma-ray pulses. The digital charge integration (DCI) method was also used as a reference-method for comparison with DCPR method. The figure-ofmerit (FOM) values which were calculated in the 50 ÷ 1100 keV electron equivalent (keVee) region showed that the DCPR method outperformed the DCI method. The FOMs of 50, 420 and 1000 keVee thresholds of DCPR method are 0.82 , 2.2 and 1.62, which are 1.55, 1.77, and 1.1 times greater than the DCI method, respectively.

A small detector with EJ-301 liquid scintillation was manufactured for the study on the neutron-gamma pulse shape discrimination. In this research, four algorithms, including Threshold crossing time (TCT), Pulse gradient analysis (PGA), Charge comparison method (CCM), and Correlation pattern recognition (CPR) were developed and compared in terms of their discrimination effectiveness between neutrons and gamma rays. The figures of merits (FOMs) obtained for 100 ÷ 2000 keVee (keV energy electron equivalent) neutron energy range show the charge comparison method was the most efficient of the four algorithms.

The interference of gamma in neutron spectra reduces the accuracy of measurement results, especially when using the scintillation detector. The digital method can be used to identify either neutron or gamma pulses. In order to select the algorithm for NE213 scintillation detector, the Matlab Simulink tool was used to simulate neutron counting system. The results show that the figure of merits (FOM) of:rise-time discrimination method (RTD), pulsed gradient analysis (PGA) method, charge comparison method (CCM), and correlation pattern method (CPM) are 1.09, 0.66, 2.21 and 1.97, respectively.