| Applications of neutron detecting technology in the fields of national defense,nuclear power,medical treatment,materials,nuclear safety,environmental protection and nuclear physics research have been well advanced,which play a significant role in China's national security,economic development and technological progress.However,it is difficult,whether in the neutron nuclear physics experiments or in the process of neutron detection in national defense,medical treatment,industry,space science and so on,to discriminate between the neutron and gamma rays,due to the sensitivity to same detectors for neutron and gamma rays,and the concurrence of both caused by interactions such as inelastic scattering between neutrons and the surroundings,radiation capture of slow neutron and so on.Therefore,it is a pivotal issue to discriminate between neutron and gamma rays from neutron-gamma mixed field in neutron detection.As an important method to improve the efficiency of neutron detection and significant indicator to evaluate the performance of neutron detectors,pulse-shape discrimination plays a crucial role in the development of neutron detection technology.With the constant improvement of detector discriminating performance and the update of digital discriminating methods,the ability of neutron-gamma discrimination is continuously improved.However,in the process of pulse-shape discrimination,the necessity to ensure that the original pulse shape from the detectors doesn't transform during acquisition and transmission,poses a serious challenge on the update of neutron-gamma discriminating equipment.Furthermore,despite the rapid development of neutron-gamma digital discriminating methods,the discrepancy,accuracy and practicability of different algorithms are still in urgent need of verification and research,especially for the research on neutron-gamma discriminating method that can be applied to the real-time pulse-shape discrimination analyzer.Inspired by present methods of neutron-gamma discrimination,concerning the special requirements of neutron-gamma discrimination in some complex radiation environments and the advantages of waveform-digitization technology in particle physics experiment,the paper targets to increase the ability of neutron-gamma discrimination,develop new methods and instrument for neutron-gamma discrimination,on the basis of the new plastic scintillator.The main contents of the paper are as follows:(1)The research selects the plastic scintillator detector EJ-276 as its subject,building an experimental platform for neutron-gamma discrimination,obtaining neutron-gamma test data from the neutron-gamma mixing field,and preprocessing the acquired pulse signal,thus it can meet the need of neutron-gamma discrimination methods.In the course of preprocessing,given the problem of neutron-gamma pulse pile-up,a correction method of pulse pile-up based on Kalman Filter is put forward.Then the ensuing theory research and simulation research are carried out.Also,the feasibility and effectiveness of this method is verified,and the correction effect of neutron-gamma pulse pile-up of which,together with its impacts on neutron-gamma discrimination,are analyzed.(2)New Neutron-gamma discriminating method which is based on Kalman Filter and fractal spectrum is put forward.At the same time,two mathematic models are constructed respectively,through which the neutron-gamma pulse-shape discrimination is achieved.A contrastive analysis has been conducted by introducing charge comparison method,which evaluates the difference,validity and practicability of the discriminating ability of four methods.Moreover,high frequency noise is also introduced to test the anti-noise ability of above four methods.(3)A neutron-gamma discriminating analyzer has been designed based on waveform-digitization technology,whose need for a clean and efficient power supply is met with the application of high integration and low noise power supply management scheme.A current-sensitive preamplifier is designed to ensure a stable conversion from current signal to voltage signal.The high-bandwidth and low-noise amplifier is adopted to realize the adjustment of neutron-gamma pulse signal and maintain its attributes of high bandwidth and quick response.Designing of a high-speed acquisition card,with high sampling rate and high-resolution ADC as its core,and combining of FMC interface with high-performance FPGA development board can facilitate the sampling and processing of nuclear pulse signal.And the correctness and feasibility of the system hardware design are comprehensively analyzed,through an evaluation of the simulation of PCB routing model and the performance of the signal acquisition card.(4)Based on high-performance FPGA,the acquisition and processing of neutron-gamma pulse signal are achieved.FPGA logic program is developed and the clock chip AD9523,high-speed acquisition chip AD9680 and high-speed serial JESD204 B protocol are configured to facilitate functions such as pulse data flow analysis,pulse recognition,data storage and pulse discrimination parameter extraction,so as to realize data acquisition,cache and signal processing of high-speed nuclear signals.At the same time,an upper computer software is developed,which can communicate with the upper computer through asynchronous serial port,to achieve the control of the data acquisition system,the receiving of measured data and the display of the discriminated data.It can also carry out real-time acquisition of nuclear pulse signals,as well as draw and display the effect diagram of pulse-shape discrimination.This article has mainly achieved the following innovations:(1)A method of pulse pile-correction based on Kalman Filter is proposed,which can achieve better effect of neutron-gamma pulse pile-up correction,improve the performance of neutron-gamma discrimination,and possess excellent anti-noise ability.(2)The neutron-gamma discrimination methods based on adaptive Kalman Filter and fractal spectrum method are proposed respectively,which,compared with the traditional charge comparison method and pulse gradient method,has better discriminating performance and anti-noise ability.In comparison,the adaptive Kalman Filter method has the best discriminating effect,while the fractal spectrum method shows the best anti-noise ability.(3)A design method of pulse shape discrimination analyzer based on waveform digitization technology is presented.The application of High-speed ADC,high-speed serial transmission protocol JESD204 B and high-performance FPGA into precise measurement of pulse shape discrimination will improve the sampling performance and measurement accuracy of the system,as well as increase the level of intelligence of neutron detection equipment. |
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