ABSTRACT The organic scintillator detector has been used in neutron detection systems with advantage of high efficiency, but they are also very sensitive to gamma.. Therefore, gamma even
Trang 1ABSTRACT
The organic scintillator detector has been used in neutron detection systems with advantage of high efficiency, but they are also very sensitive to gamma Therefore, gamma events must be identified in these radiation measurement systems to eliminate Various algorithms of neutron/gamma pulse shape discrimination (PSD) have been developed by many radiation laboratories in order to identify neutron/gamma events from the detector outputs The PSD algorithms have achieved good results in the high energy region (> 200keVee) but that still limited in the low energy region (< 200keVee) Actually, some complex PSD algorithms have been well able to distinguish between neutron and gamma pulses but these algorithms require very large hardware resources, and therefore are hardly applied for the radiation measurement systems in real-time
The goal of the present thesis is to study various PSD algorithms and to develop an algorithm that offers highly effective discrimination in the low-energy region, simple design, and low-cost The developed PSD algorithm can therefore be effortlessly applied to neutron measurement systems using organic scintillator detectors
Four PSD methods, namely the threshold crossing time, pulse gradient analysis, digital charge integration, and correlation pattern recognition, have been studied; a new method has been developed based on calculations with the reference pulses (RP) These methods have been applied to a homemade neutron spectroscopy, which is constructed by using a handcrafted organic scintillator detector, the field-programmable gate array, and the digital signal processing technique The used hardware was a DRS4 Evaluation Board, which
is compact, stable, and reliable Our obtained neutron spectroscopy is not only accurate but also can simultaneously measure neutron and gamma spectra;
Trang 2thus it shows good potentials for applying to radiation dosimeters, as well as warning/safety monitors
Among all the concerned PSD methods, our newly developed method, which is based on calculations with the RP, has the best quality: its
Figure-of-Merits (FoMs) achieved 7.3 ± 0.2 in the energy region below 200keVee and 8.2
± 0.48 in the energy region from 100 to 1600keVee, and its correct recognition
rate measured on gamma-ray sources reaches 97.2% and 99% without and with eliminating pile-pulse, respectively
Briefly, the present thesis provides important information for the development of PSD algorithms used for organic scintillator detectors In particular, a new PSD algorithm that has better quality than all the current popular algorithms has been proposed Besides, the present work also makes a crucial step forward to the domestically fabrication of high-quality and low-cost neutron/gamma spectroscopies in Vietnam
Keywords: Neutron/gamma pulse separation, neutron detector, pulse shape
discrimination, digital neutron detection system